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Segment Information (Operations By Segment) (Detail) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2017 | Jun. 30, 2016 | Jun. 30, 2017 | Jun. 30, 2016
Segment Reporting Information [Line Items] |  |  |  |
Net premiums written | $ 7,581 | $ 7,639 | $ 14,291 | $ 13,634
Net premiums earned | 7,237 | 7,405 | 14,009 | 14,002
Losses and loss expenses | 4,146 | 4,254 | 7,935 | 7,928
Policy benefits | 163 | 146 | 331 | 272
Policy acquisition costs | 1,449 | 1,560 | 2,846 | 2,973
Administrative expenses | 706 | 829 | 1,382 | 1,601
Underwriting income (loss) | 773 | 616 | 1,515 | 1,228
Net investment income | 770 | 708 | 1,515 | 1,382
Other (income) expense | (145) | (29) | (215) | (1)
Amortization of purchased intangibles | 65 | 5 | 129 | 12
Segment Income (loss) | 1,623 | 1,348 | 3,116 | 2,599
Net realized gains (losses) including OTTI | 101 | (216) | 94 | (610)
Interest expense | 147 | 153 | 301 | 299
Chubb integration expenses | 72 | 98 | 183 | 246
Income tax expense | 200 | 155 | 328 | 279
Net income | 1,305 | 726 | 2,398 | 1,165
North America Commercial P&C Insurance [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Net premiums written | 3,204 | 3,245 | 5,946 | 5,547
Net premiums earned | 3,099 | 3,148 | 6,140 | 6,044
Losses and loss expenses | 1,936 | 1,971 | 3,796 | 3,718
Policy benefits | 0 |  | 0 | 0
Policy acquisition costs | 464 | 545 | 951 | 1,027
Administrative expenses | 241 | 299 | 472 | 565
Underwriting income (loss) | 458 | 333 | 921 | 734
Net investment income | 490 | 468 | 968 | 894
Other (income) expense | (4) | (9) | 0 | (9)
Amortization of purchased intangibles | 0 | 0 | 0 | 0
Segment Income (loss) | 952 | 810 | 1,889 | 1,637
North America Personal P&C Insurance [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Net premiums written | 1,255 | 1,231 | 2,239 | 2,102
Net premiums earned | 1,093 | 1,140 | 2,179 | 2,164
Losses and loss expenses | 683 | 661 | 1,316 | 1,322
Policy benefits | 0 |  | 0 | 0
Policy acquisition costs | 230 | 269 | 447 | 518
Administrative expenses | 66 | 98 | 131 | 186
Underwriting income (loss) | 114 | 112 | 285 | 138
Net investment income | 56 | 55 | 111 | 102
Other (income) expense | 1 | 3 | 2 | 4
Amortization of purchased intangibles | 5 | 4 | 8 | 12
Segment Income (loss) | 164 | 160 | 386 | 224
North America Agricultural Insurance [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Net premiums written | 403 | 375 | 464 | 439
Net premiums earned | 344 | 327 | 358 | 350
Losses and loss expenses | 290 | 284 | 217 | 254
Policy benefits |  |  | 0 | 0
Policy acquisition costs | 27 | 25 | 26 | 29
Administrative expenses | 2 | 2 | (3) | (2)
Underwriting income (loss) | 25 | 16 | 118 | 69
Net investment income | 6 | 5 | 12 | 10
Other (income) expense | 1 | 0 | 1 | 0
Amortization of purchased intangibles | 7 | 8 | 14 | 15
Segment Income (loss) | 23 | 13 | 115 | 64
Overseas General Insurance [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Net premiums written | 2,006 | 2,031 | 4,206 | 4,072
Net premiums earned | 2,018 | 2,093 | 3,954 | 4,048
Losses and loss expenses | 964 | 1,089 | 2,035 | 2,110
Policy benefits | 0 |  | 0 | 0
Policy acquisition costs | 555 | 537 | 1,084 | 1,040
Administrative expenses | 243 | 277 | 488 | 540
Underwriting income (loss) | 256 | 190 | 347 | 358
Net investment income | 148 | 147 | 296 | 293
Other (income) expense | (3) | (5) | (4) | (10)
Amortization of purchased intangibles | 11 | 13 | 22 | 24
Segment Income (loss) | 396 | 329 | 625 | 637
Global Reinsurance [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Net premiums written | 190 | 230 | 389 | 431
Net premiums earned | 168 | 185 | 357 | 387
Losses and loss expenses | 46 | 87 | 140 | 176
Policy benefits | 0 |  | 0 | 0
Policy acquisition costs | 43 | 47 | 94 | 100
Administrative expenses | 12 | 14 | 22 | 28
Underwriting income (loss) | 67 | 37 | 101 | 83
Net investment income | 65 | 65 | 127 | 132
Other (income) expense | 1 | (2) | 1 | (3)
Amortization of purchased intangibles | 0 | 0 | 0 | 0
Segment Income (loss) | 131 | 104 | 227 | 218
Life Insurance [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Net premiums written | 523 | 527 | 1,047 | 1,043
Net premiums earned | 515 | 512 | 1,021 | 1,009
Losses and loss expenses | 182 | 147 | 375 | 324
Policy benefits | 163 | 146 | 331 | 272
Policy acquisition costs | 130 | 137 | 244 | 259
Administrative expenses | 77 | 77 | 149 | 149
Underwriting income (loss) | (37) | 5 | (78) | 5
Net investment income | 77 | 69 | 152 | 136
Other (income) expense | (12) | 0 | (41) | 6
Amortization of purchased intangibles | 0 | 0 | 1 | 1
Segment Income (loss) | 52 | 74 | 114 | 134
Corporate And Other [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Net premiums written | 0 |  | 0 | 0
Net premiums earned | 0 |  | 0 | 0
Losses and loss expenses | 45 | 15 | 56 | 24
Policy benefits | 0 |  | 0 | 0
Policy acquisition costs | 0 | 0 | 0 | 0
Administrative expenses | 65 | 62 | 123 | 135
Underwriting income (loss) | (110) | (77) | (179) | (159)
Net investment income | (72) | (101) | (151) | (185)
Other (income) expense | (129) | (16) | (174) | 11
Amortization of purchased intangibles | 42 | (20) | 84 | (40)
Segment Income (loss) | (95) | (142) | (240) | (315)
Net realized gains (losses) including OTTI | 101 | (216) | 94 | (610)
Interest expense | 147 | 153 | 301 | 299
Chubb integration expenses | 72 | 98 | 183 | 246
Income tax expense | 200 | 155 | 328 | 279
Net income | $ (413) | $ (764) | $ (958) | $ (1,749)

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