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Segment Information (Operations By Segment) (Detail) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Net premiums written |  |  |  |  |  |  |  |  |  | $ 30,579 | $ 29,244 |  | $ 28,145
Net premiums earned |  | $ 7,465 | $ 7,908 | $ 7,664 | $ 7,027 | $ 7,218 | $ 7,807 | $ 7,237 | $ 6,772 | 30,064 | 29,034 |  | 28,749
Losses and loss expenses |  | 4,610 | 4,868 | 4,487 | 4,102 | 4,272 | 6,247 | 4,146 | 3,789 | 18,067 | 18,454 |  | 16,052
Policy benefits |  | 162 | 127 | 150 | 151 | 176 | 169 | 163 | 168 | 590 | 676 |  | 588
Policy Acquisition Costs |  |  |  |  |  |  |  |  |  | 5,912 | 5,781 |  | 5,904
Administrative expenses |  |  |  |  |  |  |  |  |  | 2,886 | 2,833 |  | 3,081
Underwriting income (loss) |  |  |  |  |  |  |  |  |  | 2,609 | 1,290 |  | 3,124
Net Investment Income |  | 848 | 823 | 828 | 806 | 797 | 813 | 770 | 745 | 3,305 | 3,125 |  | 2,865
Other (Income) Expense |  |  |  |  |  |  |  |  |  | (434) | (400) |  | (222)
Amortization of Purchased Intangibles |  |  |  |  |  |  |  |  |  | 339 | 260 |  | 19
Segment Underwriting Income Loss and Net Investment Income Loss |  |  |  |  |  |  |  |  |  | 6,009 | 4,555 |  | 6,192
Realized Gain (Loss) on Marketable Securities, Cost Method Investments, and Other Investments |  |  |  |  |  |  | (10) | 101 | (7) |  | 84 |  | (145)
Net Realized Gain (Loss) |  | (687) | 19 | 18 | (2) |  |  |  |  | (652) |  |  |
Interest expense |  |  |  |  |  |  |  |  |  | 641 | 607 |  | 605
Chubb integration expenses |  |  |  |  |  |  |  |  |  | 59 | 310 |  | 492
Income tax expense (benefit) |  |  |  |  |  |  |  |  |  | 695 | (139) |  | 815
Net income |  | $ 355 | $ 1,231 | $ 1,294 | $ 1,082 | $ 1,533 | $ (70) | $ 1,305 | $ 1,093 | 3,962 | 3,861 |  | 4,135
Derivative, Gain (Loss) on Derivative, Net |  |  |  |  |  |  |  |  |  | (330) | 87 |  | (126)
Other (income) expense |  |  |  |  |  |  |  |  |  | (434) | (400) |  | (222)
(Gains) losses from fair value changes in separate account assets | [1] |  |  |  |  |  |  |  |  | (38) | 97 |  | 11
North America Commercial P&C Insurance |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Net premiums written |  |  |  |  |  |  |  |  |  | 12,485 | 12,019 | [2] | 11,740
Net premiums earned |  |  |  |  |  |  |  |  |  | 12,402 | 12,191 |  | 12,217
Losses and loss expenses |  |  |  |  |  |  |  |  |  | 8,000 | 8,287 |  | 7,439
Policy benefits |  |  |  |  |  |  |  |  |  | 0 | 0 |  | 0
Policy Acquisition Costs |  |  |  |  |  |  |  |  |  | 1,829 | 1,873 |  | 2,023
Administrative expenses |  |  |  |  |  |  |  |  |  | 966 | 981 |  | 1,125
Underwriting income (loss) |  |  |  |  |  |  |  |  |  | 1,607 | 1,050 |  | 1,630
Net Investment Income |  |  |  |  |  |  |  |  |  | 2,033 | 1,961 |  | 1,860
Other (Income) Expense |  |  |  |  |  |  |  |  |  | (25) | 1 |  | (2)
Amortization of Purchased Intangibles |  |  |  |  |  |  |  |  |  | 0 | 0 |  | 0
Segment Underwriting Income Loss and Net Investment Income Loss |  |  |  |  |  |  |  |  |  | 3,665 | 3,010 |  | 3,492
North American Personal P&C [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Net premiums written |  |  |  |  |  |  |  |  |  | 4,674 | 4,533 |  | 4,153
Net premiums earned |  |  |  |  |  |  |  |  |  | 4,593 | 4,399 |  | 4,319
Losses and loss expenses |  |  |  |  |  |  |  |  |  | 3,229 | 3,265 |  | 2,558
Policy benefits |  |  |  |  |  |  |  |  |  | 0 | 0 |  | 0
Policy Acquisition Costs |  |  |  |  |  |  |  |  |  | 939 | 899 |  | 966
Administrative expenses |  |  |  |  |  |  |  |  |  | 269 | 264 |  | 363
Underwriting income (loss) |  |  |  |  |  |  |  |  |  | 156 | (29) |  | 432
Net Investment Income |  |  |  |  |  |  |  |  |  | 236 | 226 |  | 207
Other (Income) Expense |  |  |  |  |  |  |  |  |  | 1 | 4 |  | 6
Amortization of Purchased Intangibles |  |  |  |  |  |  |  |  |  | 13 | 16 |  | 19
Segment Underwriting Income Loss and Net Investment Income Loss |  |  |  |  |  |  |  |  |  | 378 | 177 |  | 614
North America Agricultural Insurance |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Net premiums written |  |  |  |  |  |  |  |  |  | 1,577 | 1,516 |  | 1,328
Net premiums earned |  |  |  |  |  |  |  |  |  | 1,569 | 1,508 |  | 1,316
Losses and loss expenses |  |  |  |  |  |  |  |  |  | 1,111 | 1,036 |  | 893
Policy benefits |  |  |  |  |  |  |  |  |  | 0 | 0 |  | 0
Policy Acquisition Costs |  |  |  |  |  |  |  |  |  | 79 | 81 |  | 83
Administrative expenses |  |  |  |  |  |  |  |  |  | (9) | (8) |  | (6)
Underwriting income (loss) |  |  |  |  |  |  |  |  |  | 388 | 399 |  | 346
Net Investment Income |  |  |  |  |  |  |  |  |  | 28 | 25 |  | 20
Other (Income) Expense |  |  |  |  |  |  |  |  |  | 2 | 2 |  | 1
Amortization of Purchased Intangibles |  |  |  |  |  |  |  |  |  | 28 | 29 |  | 29
Segment Underwriting Income Loss and Net Investment Income Loss |  |  |  |  |  |  |  |  |  | 386 | 393 |  | 336
Segment Income Loss Including Gains Losses On Crop Derivatives |  |  |  |  |  |  |  |  |  | 385 |  |  |
Derivative, Gain (Loss) on Derivative, Net |  |  |  |  |  |  |  |  |  | 3 |  |  |
Overseas General Insurance |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Net premiums written |  |  |  |  |  |  |  |  |  | 8,902 | 8,350 | [2] | 8,124
Net premiums earned |  |  |  |  |  |  |  |  |  | 8,612 | 8,131 |  | 8,132
Losses and loss expenses |  |  |  |  |  |  |  |  |  | 4,429 | 4,281 |  | 4,005
Policy benefits |  |  |  |  |  |  |  |  |  | 0 | 0 |  | 0
Policy Acquisition Costs |  |  |  |  |  |  |  |  |  | 2,346 | 2,221 |  | 2,136
Administrative expenses |  |  |  |  |  |  |  |  |  | 1,014 | 982 |  | 1,057
Underwriting income (loss) |  |  |  |  |  |  |  |  |  | 823 | 647 |  | 934
Net Investment Income |  |  |  |  |  |  |  |  |  | 619 | 610 |  | 600
Other (Income) Expense |  |  |  |  |  |  |  |  |  | 0 | (4) |  | (11)
Amortization of Purchased Intangibles |  |  |  |  |  |  |  |  |  | 41 | 45 |  | 48
Segment Underwriting Income Loss and Net Investment Income Loss |  |  |  |  |  |  |  |  |  | 1,401 | 1,216 |  | 1,497
Global Reinsurance |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Net premiums written |  |  |  |  |  |  |  |  |  | 671 | 685 |  | 676
Net premiums earned |  |  |  |  |  |  |  |  |  | 670 | 704 |  | 710
Losses and loss expenses |  |  |  |  |  |  |  |  |  | 479 | 561 |  | 325
Policy benefits |  |  |  |  |  |  |  |  |  | 0 | 0 |  | 0
Policy Acquisition Costs |  |  |  |  |  |  |  |  |  | 162 | 177 |  | 187
Administrative expenses |  |  |  |  |  |  |  |  |  | 41 | 44 |  | 52
Underwriting income (loss) |  |  |  |  |  |  |  |  |  | (12) | (78) |  | 146
Net Investment Income |  |  |  |  |  |  |  |  |  | 257 | 273 |  | 263
Other (Income) Expense |  |  |  |  |  |  |  |  |  | (32) | (1) |  | (4)
Amortization of Purchased Intangibles |  |  |  |  |  |  |  |  |  | 0 | 0 |  | 0
Segment Underwriting Income Loss and Net Investment Income Loss |  |  |  |  |  |  |  |  |  | 277 | 196 |  | 413
Life Insurance |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Net premiums written |  |  |  |  |  |  |  |  |  | 2,270 | 2,141 |  | 2,124
Net premiums earned |  |  |  |  |  |  |  |  |  | 2,218 | 2,101 |  | 2,055
Losses and loss expenses |  |  |  |  |  |  |  |  |  | 766 | 739 |  | 663
Policy benefits |  |  |  |  |  |  |  |  |  | 590 | 676 |  | 588
Policy Acquisition Costs |  |  |  |  |  |  |  |  |  | 557 | 530 |  | 509
Administrative expenses |  |  |  |  |  |  |  |  |  | 310 | 303 |  | 307
Underwriting income (loss) |  |  |  |  |  |  |  |  |  | (5) | (147) |  | (12)
Net Investment Income |  |  |  |  |  |  |  |  |  | 341 | 313 |  | 283
Other (Income) Expense |  |  |  |  |  |  |  |  |  | 26 | (84) |  | 5
Amortization of Purchased Intangibles |  |  |  |  |  |  |  |  |  | 2 | 2 |  | 3
Segment Underwriting Income Loss and Net Investment Income Loss |  |  |  |  |  |  |  |  |  | 308 | 248 |  | 263
Management underwriting income loss Insurance |  |  |  |  |  |  |  |  |  | 298 |  |  |
(Gains) losses from fair value changes in separate account assets |  |  |  |  |  |  |  |  |  | 38 |  |  |
Corporate and Other |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Net premiums written |  |  |  |  |  |  |  |  |  | 0 | 0 |  | 0
Net premiums earned |  |  |  |  |  |  |  |  |  | 0 | 0 |  | 0
Losses and loss expenses |  |  |  |  |  |  |  |  |  | 53 | 285 |  | 169
Policy benefits |  |  |  |  |  |  |  |  |  | 0 | 0 |  | 0
Policy Acquisition Costs |  |  |  |  |  |  |  |  |  | 0 | 0 |  | 0
Administrative expenses |  |  |  |  |  |  |  |  |  | 295 | 267 |  | 183
Underwriting income (loss) |  |  |  |  |  |  |  |  |  | (348) | (552) |  | (352)
Net Investment Income |  |  |  |  |  |  |  |  |  | (209) | (283) |  | (368)
Other (Income) Expense |  |  |  |  |  |  |  |  |  | (406) | (318) |  | (217)
Amortization of Purchased Intangibles |  |  |  |  |  |  |  |  |  | 255 | 168 |  | (80)
Segment Underwriting Income Loss and Net Investment Income Loss |  |  |  |  |  |  |  |  |  | (406) | (685) |  | (423)
Realized Gain (Loss) on Marketable Securities, Cost Method Investments, and Other Investments |  |  |  |  |  |  |  |  |  |  | 84 |  | (145)
Net Realized Gain (Loss) |  |  |  |  |  |  |  |  |  | (652) |  |  |
Interest expense |  |  |  |  |  |  |  |  |  | 641 | 607 |  | 605
Chubb integration expenses |  |  |  |  |  |  |  |  |  | 59 | 310 |  | 492
Income tax expense (benefit) |  |  |  |  |  |  |  |  |  | 695 | (139) |  | 815
Net income |  |  |  |  |  |  |  |  |  | $ (2,453) | $ (1,379) |  | $ (2,480)
[1] | Related to (gains) losses from fair value changes in separate account assets that do not qualify for separate account reporting under GAAP.
[2] | For the Year Ended December 31, 2017 (in millions of U.S. dollars)North America Commercial P&C Insurance North America Personal P&C Insurance North America Agricultural Insurance Overseas General Insurance GlobalReinsurance Life Insurance Corporate ChubbConsolidatedNet premiums written$12,019 $4,533 $1,516 $8,350 $685 $2,141 $— $29,244Net premiums earned12,191 4,399 1,508 8,131 704 2,101 — 29,034Losses and loss expenses8,287 3,265 1,036 4,281 561 739 285 18,454Policy benefits— — — — — 676 — 676Policy acquisition costs1,873 899 81 2,221 177 530 — 5,781Administrative expenses981 264 (8) 982 44 303 267 2,833Underwriting income (loss)1,050 (29) 399 647 (78) (147) (552) 1,290Net investment income (loss)1,961 226 25 610 273 313 (283) 3,125Other (income) expense1 4 2 (4) (1) (84) (318) (400)Amortization expense of purchased intangibles— 16 29 45 — 2 168 260Segment income (loss)$3,010 $177 $393 $1,216 $196 $248 $(685) $4,555Net realized gains (losses) including OTTI 84 84Interest expense 607 607Chubb integration expense 310 310Income tax benefit (139) (139)Net income (loss) $(1,379) $3,861

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