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Unpaid losses and loss expenses Unpaid Losses and loss expenses, claims development (Cumulative Net incurred Loss and Allocated Loss Adjustment Expense) (Details) number in Thousands, $ in Millions | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) | Dec. 31, 2014 USD ($) | Dec. 31, 2013 USD ($) | Dec. 31, 2012 USD ($) | Dec. 31, 2011 USD ($) | Dec. 31, 2010 USD ($) | Dec. 31, 2009 USD ($) | Dec. 31, 2008 USD ($)
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Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net | $ 46,700 |  |  |  |  |  |  |  |  |
North America Commercial P&C Insurance - Workers' Compensation [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | 11,327 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | 4,937 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented | 2,483 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net | 8,873 |  |  |  |  |  |  |  |  |
North America Commercial P&C Insurance - Liability [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | 34,121 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | 18,919 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented | 1,429 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net | 16,631 |  |  |  |  |  |  |  |  |
North America Commercial P&C Insurance - Other Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | 5,185 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | 3,633 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented | 237 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net | 1,789 |  |  |  |  |  |  |  |  |
North America Commercial P&C Insurance - Non-Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | 17,229 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | 14,854 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented | 23 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net | 2,398 |  |  |  |  |  |  |  |  |
North America Personal P&C Insurance [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | 21,564 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | 19,168 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented | 25 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net | 2,421 |  |  |  |  |  |  |  |  |
Overseas General Insurance - Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | 12,673 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | 6,997 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented | 350 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net | 6,026 |  |  |  |  |  |  |  |  |
Overseas General Insurance - Non-Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | 18,445 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | 15,961 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented | 65 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net | 2,549 |  |  |  |  |  |  |  |  |
Global Reinsurance - Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | 3,320 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | 2,339 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented | 359 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net | 1,340 |  |  |  |  |  |  |  |  |
Global Reinsurance - Non-Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | 2,172 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | 1,816 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented | 15 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net | 371 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2008 [Member] | North America Commercial P&C Insurance - Workers' Compensation [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | 993 | $ 986 | $ 1,004 | $ 1,009 | $ 1,010 | $ 1,036 | $ 1,037 | $ 1,043 | $ 1,042 | $ 1,084
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 214 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 651 | 632 | 607 | 578 | 546 | 503 | 439 | 371 | 275 | 124
Short-duration Insurance Contracts, Number of Reported Claims | 333 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2008 [Member] | North America Commercial P&C Insurance - Liability [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 3,157 | 3,174 | 3,278 | 3,352 | 3,412 | 3,652 | 3,791 | 3,812 | 3,823 | 3,792
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 245 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 2,836 | 2,753 | 2,657 | 2,558 | 2,323 | 1,992 | 1,643 | 1,110 | 580 | 147
Short-duration Insurance Contracts, Number of Reported Claims | 21 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2008 [Member] | North America Commercial P&C Insurance - Other Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 637 | 641 | 646 | 643 | 647 | 644 | 661 | 700 | 733 | 693
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 13 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 617 | 618 | 610 | 602 | 591 | 566 | 520 | 446 | 342 | 144
Short-duration Insurance Contracts, Number of Reported Claims | 20 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2008 [Member] | North America Commercial P&C Insurance - Non-Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 1,859 | 1,863 | 1,865 | 1,877 | 1,881 | 1,890 | 1,901 | 1,916 | 1,941 | 1,999
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 5 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 1,851 | 1,848 | 1,847 | 1,838 | 1,832 | 1,823 | 1,794 | 1,744 | 1,622 | 965
Short-duration Insurance Contracts, Number of Reported Claims | 999 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2008 [Member] | North America Personal P&C Insurance [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 1,659 | 1,661 | 1,661 | 1,670 | 1,677 | 1,695 | 1,724 | 1,749 | 1,779 | 1,779
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 5 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 1,651 | 1,651 | 1,647 | 1,644 | 1,638 | 1,622 | 1,586 | 1,521 | 1,409 | 975
Short-duration Insurance Contracts, Number of Reported Claims | 139 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2008 [Member] | Overseas General Insurance - Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 1,281 | 1,330 | 1,315 | 1,336 | 1,408 | 1,453 | 1,444 | 1,423 | 1,334 | 1,220
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 81 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 1,116 | 1,083 | 1,029 | 971 | 895 | 790 | 642 | 472 | 306 | 121
Short-duration Insurance Contracts, Number of Reported Claims | 39 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2008 [Member] | Overseas General Insurance - Non-Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 1,504 | 1,508 | 1,519 | 1,524 | 1,527 | 1,553 | 1,547 | 1,563 | 1,608 | 1,609
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 25 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 1,484 | 1,477 | 1,477 | 1,469 | 1,461 | 1,451 | 1,428 | 1,360 | 1,218 | 646
Short-duration Insurance Contracts, Number of Reported Claims | 539 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2008 [Member] | Global Reinsurance - Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 399 | 401 | 404 | 408 | 407 | 428 | 431 | 439 | 420 | 399
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 48 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 315 | 305 | 295 | 277 | 253 | 220 | 176 | 131 | 77 | 33
Short-duration Insurance Contracts, Number of Reported Claims | 1 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2008 [Member] | Global Reinsurance - Non-Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 286 | 285 | 284 | 287 | 286 | 286 | 292 | 301 | 310 | 316
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 2 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 280 | 280 | 280 | 278 | 276 | 274 | 260 | 228 | 177 | $ 79
Short-duration Insurance Contracts, Number of Reported Claims | 0 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2009 [Member] | North America Commercial P&C Insurance - Workers' Compensation [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 965 | 972 | 966 | 977 | 980 | 990 | 997 | 998 | 1,029 |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 233 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 617 | 597 | 550 | 519 | 475 | 416 | 348 | 258 | 107 |
Short-duration Insurance Contracts, Number of Reported Claims | 282 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2009 [Member] | North America Commercial P&C Insurance - Liability [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 3,103 | 3,244 | 3,316 | 3,392 | 3,642 | 3,743 | 3,770 | 3,783 | 3,798 |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 250 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 2,730 | 2,678 | 2,545 | 2,357 | 2,019 | 1,672 | 1,160 | 587 | 135 |
Short-duration Insurance Contracts, Number of Reported Claims | 21 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2009 [Member] | North America Commercial P&C Insurance - Other Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 441 | 445 | 447 | 454 | 488 | 531 | 550 | 584 | 594 |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 2 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 428 | 423 | 414 | 402 | 374 | 337 | 287 | 206 | 70 |
Short-duration Insurance Contracts, Number of Reported Claims | 15 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2009 [Member] | North America Commercial P&C Insurance - Non-Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 1,194 | 1,195 | 1,198 | 1,198 | 1,205 | 1,222 | 1,251 | 1,307 | 1,310 |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 9 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 1,181 | 1,181 | 1,179 | 1,171 | 1,163 | 1,149 | 1,125 | 1,035 | 620 |
Short-duration Insurance Contracts, Number of Reported Claims | 1,125 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2009 [Member] | North America Personal P&C Insurance [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 1,533 | 1,534 | 1,538 | 1,538 | 1,545 | 1,554 | 1,568 | 1,598 | 1,611 |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 7 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 1,523 | 1,521 | 1,513 | 1,503 | 1,486 | 1,439 | 1,347 | 1,236 | 887 |
Short-duration Insurance Contracts, Number of Reported Claims | 125 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2009 [Member] | Overseas General Insurance - Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 1,202 | 1,256 | 1,257 | 1,365 | 1,482 | 1,485 | 1,474 | 1,425 | 1,284 |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 76 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 1,020 | 993 | 896 | 824 | 763 | 667 | 524 | 341 | 123 |
Short-duration Insurance Contracts, Number of Reported Claims | 39 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2009 [Member] | Overseas General Insurance - Non-Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 1,366 | 1,366 | 1,377 | 1,377 | 1,395 | 1,415 | 1,446 | 1,534 | 1,564 |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 3 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 1,343 | 1,344 | 1,341 | 1,335 | 1,324 | 1,300 | 1,233 | 1,095 | 602 |
Short-duration Insurance Contracts, Number of Reported Claims | 518 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2009 [Member] | Global Reinsurance - Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 316 | 320 | 331 | 347 | 366 | 370 | 363 | 351 | 319 |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 24 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 256 | 241 | 227 | 209 | 187 | 154 | 116 | 79 | 34 |
Short-duration Insurance Contracts, Number of Reported Claims | 1 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2009 [Member] | Global Reinsurance - Non-Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 139 | 139 | 139 | 141 | 144 | 150 | 152 | 172 | 141 |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 3 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 134 | 134 | 134 | 134 | 132 | 129 | 122 | 106 | $ 52 |
Short-duration Insurance Contracts, Number of Reported Claims | 0 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2010 [Member] | North America Commercial P&C Insurance - Workers' Compensation [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 1,020 | 1,028 | 1,052 | 1,064 | 1,065 | 1,050 | 1,037 | 1,049 |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 262 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 641 | 617 | 592 | 551 | 493 | 411 | 300 | 123 |  |
Short-duration Insurance Contracts, Number of Reported Claims | 304 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2010 [Member] | North America Commercial P&C Insurance - Liability [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 3,107 | 3,128 | 3,250 | 3,419 | 3,559 | 3,601 | 3,583 | 3,578 |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 423 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 2,527 | 2,426 | 2,259 | 1,893 | 1,559 | 1,108 | 611 | 126 |  |
Short-duration Insurance Contracts, Number of Reported Claims | 20 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2010 [Member] | North America Commercial P&C Insurance - Other Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 489 | 477 | 475 | 503 | 543 | 598 | 604 | 610 |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 33 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 449 | 444 | 434 | 392 | 364 | 322 | 236 | 97 |  |
Short-duration Insurance Contracts, Number of Reported Claims | 15 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2010 [Member] | North America Commercial P&C Insurance - Non-Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 1,410 | 1,416 | 1,420 | 1,428 | 1,430 | 1,466 | 1,543 | 1,507 |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 9 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 1,397 | 1,396 | 1,393 | 1,384 | 1,359 | 1,323 | 1,223 | 724 |  |
Short-duration Insurance Contracts, Number of Reported Claims | 1,059 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2010 [Member] | North America Personal P&C Insurance [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 1,822 | 1,825 | 1,830 | 1,834 | 1,838 | 1,855 | 1,878 | 1,870 |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 9 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 1,811 | 1,805 | 1,793 | 1,772 | 1,729 | 1,670 | 1,522 | 1,153 |  |
Short-duration Insurance Contracts, Number of Reported Claims | 149 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2010 [Member] | Overseas General Insurance - Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 1,178 | 1,183 | 1,312 | 1,365 | 1,430 | 1,358 | 1,311 | 1,231 |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 97 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 938 | 883 | 831 | 740 | 629 | 481 | 277 | 109 |  |
Short-duration Insurance Contracts, Number of Reported Claims | 41 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2010 [Member] | Overseas General Insurance - Non-Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 1,643 | 1,660 | 1,673 | 1,687 | 1,693 | 1,705 | 1,734 | 1,713 |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 13 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 1,604 | 1,603 | 1,596 | 1,583 | 1,543 | 1,480 | 1,276 | 698 |  |
Short-duration Insurance Contracts, Number of Reported Claims | 561 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2010 [Member] | Global Reinsurance - Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 402 | 416 | 426 | 432 | 443 | 432 | 421 | 401 |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 55 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 307 | 292 | 274 | 249 | 221 | 179 | 125 | 56 |  |
Short-duration Insurance Contracts, Number of Reported Claims | 1 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2010 [Member] | Global Reinsurance - Non-Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 225 | 225 | 224 | 222 | 218 | 224 | 235 | 200 |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 5 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 217 | 214 | 216 | 205 | 200 | 188 | 162 | $ 56 |  |
Short-duration Insurance Contracts, Number of Reported Claims | 0 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2011 [Member] | North America Commercial P&C Insurance - Workers' Compensation [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 1,012 | 1,022 | 1,053 | 1,049 | 1,046 | 1,030 | 1,037 |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 294 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 595 | 567 | 533 | 484 | 411 | 294 | 119 |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 287 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2011 [Member] | North America Commercial P&C Insurance - Liability [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 3,383 | 3,498 | 3,593 | 3,664 | 3,629 | 3,585 | 3,500 |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 589 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 2,659 | 2,476 | 2,214 | 1,805 | 1,209 | 652 | 160 |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 20 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2011 [Member] | North America Commercial P&C Insurance - Other Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 513 | 521 | 530 | 545 | 578 | 586 | 577 |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 33 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 466 | 461 | 437 | 400 | 341 | 235 | 86 |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 16 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2011 [Member] | North America Commercial P&C Insurance - Non-Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 1,838 | 1,843 | 1,839 | 1,859 | 1,881 | 1,938 | 1,963 |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 15 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 1,816 | 1,811 | 1,787 | 1,777 | 1,718 | 1,573 | 939 |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 1,053 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2011 [Member] | North America Personal P&C Insurance [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 2,159 | 2,160 | 2,164 | 2,173 | 2,185 | 2,210 | 2,208 |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 13 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 2,138 | 2,129 | 2,105 | 2,051 | 1,971 | 1,835 | 1,360 |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 168 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2011 [Member] | Overseas General Insurance - Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 1,094 | 1,109 | 1,176 | 1,262 | 1,270 | 1,277 | 1,272 |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 157 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 795 | 719 | 638 | 534 | 400 | 250 | 91 |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 42 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2011 [Member] | Overseas General Insurance - Non-Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 1,901 | 1,908 | 1,920 | 1,939 | 1,978 | 2,035 | 1,950 |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 7 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 1,841 | 1,832 | 1,817 | 1,786 | 1,728 | 1,520 | 793 |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 579 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2011 [Member] | Global Reinsurance - Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 415 | 419 | 429 | 434 | 431 | 416 | 409 |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 45 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 311 | 291 | 267 | 236 | 195 | 146 | 70 |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 1 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2011 [Member] | Global Reinsurance - Non-Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 264 | 264 | 263 | 262 | 272 | 275 | 274 |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 1 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 258 | 255 | 251 | 232 | 207 | 176 | $ 85 |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 0 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2012 [Member] | North America Commercial P&C Insurance - Workers' Compensation [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 989 | 1,011 | 1,040 | 1,030 | 1,011 | 1,050 |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 326 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 532 | 486 | 436 | 365 | 271 | 111 |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 288 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2012 [Member] | North America Commercial P&C Insurance - Liability [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 3,426 | 3,524 | 3,564 | 3,613 | 3,628 | 3,552 |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 856 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 2,326 | 2,092 | 1,680 | 1,172 | 656 | 166 |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 20 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2012 [Member] | North America Commercial P&C Insurance - Other Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 517 | 518 | 559 | 575 | 604 | 632 |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 27 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 470 | 435 | 386 | 319 | 223 | 69 |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 16 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2012 [Member] | North America Commercial P&C Insurance - Non-Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 1,848 | 1,861 | 1,866 | 1,884 | 1,918 | 2,034 |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 11 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 1,822 | 1,795 | 1,766 | 1,698 | 1,577 | 715 |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 1,037 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2012 [Member] | North America Personal P&C Insurance [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 2,186 | 2,185 | 2,191 | 2,183 | 2,183 | 2,185 |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 9 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 2,149 | 2,117 | 2,063 | 1,957 | 1,806 | 1,176 |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 173 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2012 [Member] | Overseas General Insurance - Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 1,345 | 1,363 | 1,367 | 1,348 | 1,281 | 1,311 |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 279 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 856 | 714 | 598 | 443 | 254 | 77 |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 42 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2012 [Member] | Overseas General Insurance - Non-Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 1,650 | 1,661 | 1,667 | 1,723 | 1,764 | 1,775 |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 34 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 1,572 | 1,562 | 1,539 | 1,479 | 1,284 | 716 |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 600 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2012 [Member] | Global Reinsurance - Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 372 | 379 | 394 | 391 | 383 | 387 |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 23 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 308 | 292 | 261 | 222 | 167 | 77 |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 0 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2012 [Member] | Global Reinsurance - Non-Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 187 | 189 | 191 | 200 | 210 | 232 |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 2 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 177 | 172 | 166 | 156 | 129 | $ 44 |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 0 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2013 [Member] | North America Commercial P&C Insurance - Workers' Compensation [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 1,085 | 1,127 | 1,122 | 1,108 | 1,109 |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 368 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 553 | 506 | 422 | 286 | 107 |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 300 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2013 [Member] | North America Commercial P&C Insurance - Liability [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 3,430 | 3,532 | 3,542 | 3,541 | 3,546 |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 1,090 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 2,007 | 1,597 | 1,192 | 548 | 130 |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 20 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2013 [Member] | North America Commercial P&C Insurance - Other Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 468 | 515 | 522 | 530 | 526 |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 60 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 385 | 348 | 271 | 197 | 69 |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 18 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2013 [Member] | North America Commercial P&C Insurance - Non-Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 1,340 | 1,360 | 1,337 | 1,424 | 1,434 |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 18 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 1,311 | 1,285 | 1,237 | 1,138 | 651 |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 1,074 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2013 [Member] | North America Personal P&C Insurance [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 1,924 | 1,899 | 1,896 | 1,888 | 1,860 |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 41 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 1,843 | 1,786 | 1,687 | 1,504 | 1,043 |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 126 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2013 [Member] | Overseas General Insurance - Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 1,270 | 1,330 | 1,284 | 1,284 | 1,289 |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 314 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 727 | 584 | 432 | 272 | 90 |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 42 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2013 [Member] | Overseas General Insurance - Non-Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 1,730 | 1,739 | 1,787 | 1,859 | 1,868 |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 62 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 1,612 | 1,574 | 1,541 | 1,340 | 738 |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 622 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2013 [Member] | Global Reinsurance - Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 331 | 330 | 330 | 327 | 321 |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 41 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 242 | 222 | 186 | 143 | 65 |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 0 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2013 [Member] | Global Reinsurance - Non-Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 144 | 143 | 149 | 160 | 163 |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 5 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 133 | 131 | 121 | 103 | $ 46 |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 0 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2014 [Member] | North America Commercial P&C Insurance - Workers' Compensation [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 1,214 | 1,217 | 1,201 | 1,207 |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 553 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 484 | 410 | 295 | 113 |  |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 337 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2014 [Member] | North America Commercial P&C Insurance - Liability [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 3,717 | 3,674 | 3,585 | 3,535 |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 1,526 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 1,804 | 1,250 | 679 | 164 |  |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 21 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2014 [Member] | North America Commercial P&C Insurance - Other Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 594 | 579 | 581 | 592 |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 147 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 391 | 317 | 220 | 80 |  |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 17 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2014 [Member] | North America Commercial P&C Insurance - Non-Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 1,561 | 1,581 | 1,663 | 1,647 |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 29 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 1,505 | 1,484 | 1,373 | 820 |  |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 1,102 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2014 [Member] | North America Personal P&C Insurance [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 2,145 | 2,192 | 2,206 | 2,205 |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 29 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 2,034 | 1,925 | 1,764 | 1,310 |  |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 135 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2014 [Member] | Overseas General Insurance - Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 1,388 | 1,377 | 1,366 | 1,295 |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 506 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 614 | 481 | 299 | 117 |  |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 43 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2014 [Member] | Overseas General Insurance - Non-Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 1,959 | 1,985 | 2,048 | 1,975 |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 72 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 1,782 | 1,715 | 1,497 | 800 |  |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 594 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2014 [Member] | Global Reinsurance - Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 343 | 340 | 334 | 333 |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 46 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 249 | 218 | 185 | 92 |  |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 0 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2014 [Member] | Global Reinsurance - Non-Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 182 | 179 | 179 | 163 |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 9 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 162 | 151 | 128 | $ 65 |  |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 0 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2015 [Member] | North America Commercial P&C Insurance - Workers' Compensation [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 1,271 | 1,259 | 1,282 |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 631 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 418 | 301 | 116 |  |  |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 339 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2015 [Member] | North America Commercial P&C Insurance - Liability [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 3,818 | 3,708 | 3,559 |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 1,941 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 1,206 | 605 | 138 |  |  |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 23 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2015 [Member] | North America Commercial P&C Insurance - Other Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 501 | 469 | 486 |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 191 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 215 | 137 | 47 |  |  |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 15 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2015 [Member] | North America Commercial P&C Insurance - Non-Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 1,650 | 1,746 | 1,737 |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 83 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 1,488 | 1,343 | 726 |  |  |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 1,173 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2015 [Member] | North America Personal P&C Insurance [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 2,560 | 2,549 | 2,494 |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 126 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 2,270 | 2,083 | 1,499 |  |  |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 139 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2015 [Member] | Overseas General Insurance - Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 1,353 | 1,324 | 1,223 |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 542 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 504 | 296 | 92 |  |  |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 45 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2015 [Member] | Overseas General Insurance - Non-Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 2,195 | 2,243 | 2,111 |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 157 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 1,873 | 1,638 | 901 |  |  |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 627 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2015 [Member] | Global Reinsurance - Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 300 | 289 | 285 |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 47 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 191 | 159 | 90 |  |  |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 0 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2015 [Member] | Global Reinsurance - Non-Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 161 | 154 | 146 |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 8 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 132 | 103 | $ 56 |  |  |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 0 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2016 [Member] | North America Commercial P&C Insurance - Workers' Compensation [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 1,367 | 1,367 |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 806 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 326 | 122 |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 310 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2016 [Member] | North America Commercial P&C Insurance - Liability [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 3,594 | 3,533 |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 2,381 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 663 | 171 |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 24 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2016 [Member] | North America Commercial P&C Insurance - Other Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 494 | 503 |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 249 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 146 | 52 |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 15 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2016 [Member] | North America Commercial P&C Insurance - Non-Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 1,888 | 1,911 |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 168 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 1,504 | 846 |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 1,293 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2016 [Member] | North America Personal P&C Insurance [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 2,542 | 2,439 |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 248 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 2,051 | 1,453 |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 140 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2016 [Member] | Overseas General Insurance - Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 1,333 | 1,227 |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 749 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 328 | 127 |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 45 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2016 [Member] | Overseas General Insurance - Non-Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 2,148 | 2,164 |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 19 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 1,752 | 1,083 |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 637 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2016 [Member] | Global Reinsurance - Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 228 | 224 |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 63 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 113 | 57 |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 0 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2016 [Member] | Global Reinsurance - Non-Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 188 | 182 |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 17 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 132 | $ 57 |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 0 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2017 [Member] | North America Commercial P&C Insurance - Workers' Compensation [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 1,411 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 1,080 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 120 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 307 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2017 [Member] | North America Commercial P&C Insurance - Liability [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 3,386 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 2,994 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 161 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 19 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2017 [Member] | North America Commercial P&C Insurance - Other Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 531 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 387 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 66 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 13 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2017 [Member] | North America Commercial P&C Insurance - Non-Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 2,641 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 1,089 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 979 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 1,175 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2017 [Member] | North America Personal P&C Insurance [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 3,034 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 725 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 1,698 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 123 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2017 [Member] | Overseas General Insurance - Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 1,229 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 968 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 99 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 34 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2017 [Member] | Overseas General Insurance - Non-Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 2,349 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 307 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 1,098 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 616 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2017 [Member] | Global Reinsurance - Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 214 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 121 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 47 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 0 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Accident Year 2017 [Member] | Global Reinsurance - Non-Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | $ 396 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net | 82 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | $ 191 |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Number of Reported Claims | 0 |  |  |  |  |  |  |  |  |

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