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Segment Information (Operations By Segment) (Detail) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017
Segment Reporting Information [Line Items] |  |  |  |  |  |
Net premiums written | $ 8,110 | $ 7,902 |  | $ 23,229 | $ 22,193 |
Net premiums earned | 7,908 | 7,807 |  | 22,599 | 21,816 |
Losses and loss expenses | 4,868 | 6,247 |  | 13,457 | 14,182 |
Policy benefits | 127 | 169 |  | 428 | 500 |
Policy acquisition costs | 1,504 | 1,488 |  | 4,432 | 4,334 |
Administrative expenses | 719 | 714 |  | 2,158 | 2,096 |
Underwriting income (loss) | 690 | (811) |  | 2,124 | 704 |
Net investment income (loss) | 823 | 813 |  | 2,457 | 2,328 |
Other (income) expense | (145) | (118) |  | (307) | (333) |
Amortization of purchased intangibles | 83 | 65 |  | 253 | 194 |
Segment Income (loss) | 1,575 | 55 |  | 4,635 | 3,171 |
Net realized gains (losses) including OTTI | 19 | (10) |  | 35 | 84 |
Interest expense | 164 | 150 |  | 488 | 451 |
Chubb integration expenses | 16 | 50 |  | 39 | 233 |
Income tax expense | 183 | (85) |  | 536 | 243 |
Net income (loss) | 1,231 | (70) |  | 3,607 | 2,328 |
Prior Period Reclassification Adjustment |  | 3 |  |  | 16 |
North America Commercial P&C Insurance [Member] |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Net premiums written | 3,199 | 3,086 | [1] | 9,342 | 9,019 | [2]
Net premiums earned | 3,019 | 3,016 |  | 9,325 | 9,156 |
Losses and loss expenses | 1,881 | 2,580 |  | 5,873 | 6,376 |
Policy benefits | 0 | 0 |  | 0 | 0 |
Policy acquisition costs | 458 | 469 |  | 1,378 | 1,420 |
Administrative expenses | 251 | 256 |  | 735 | 728 |
Underwriting income (loss) | 429 | (289) |  | 1,339 | 632 |
Net investment income (loss) | 503 | 497 |  | 1,516 | 1,465 |
Other (income) expense | (1) | (4) |  | (20) | (4) |
Amortization of purchased intangibles | 0 | 0 |  | 0 | 0 |
Segment Income (loss) | 933 | 212 |  | 2,875 | 2,101 |
North America Personal P&C Insurance [Member] |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Net premiums written | 1,218 | 1,194 |  | 3,601 | 3,433 |
Net premiums earned | 1,167 | 1,117 |  | 3,463 | 3,296 |
Losses and loss expenses | 860 | 1,062 |  | 2,474 | 2,378 |
Policy benefits | 0 | 0 |  | 0 | 0 |
Policy acquisition costs | 236 | 226 |  | 701 | 673 |
Administrative expenses | 69 | 61 |  | 202 | 192 |
Underwriting income (loss) | 2 | (232) |  | 86 | 53 |
Net investment income (loss) | 59 | 57 |  | 177 | 168 |
Other (income) expense | 0 | 1 |  | 1 | 3 |
Amortization of purchased intangibles | 4 | 4 |  | 10 | 12 |
Segment Income (loss) | 57 | (180) |  | 252 | 206 |
North America Agricultural Insurance [Member] |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Net premiums written | 884 | 926 |  | 1,380 | 1,390 |
Net premiums earned | 857 | 898 |  | 1,251 | 1,256 |
Losses and loss expenses | 719 | 759 |  | 955 | 976 |
Policy benefits | 0 | 0 |  | 0 | 0 |
Policy acquisition costs | 49 | 49 |  | 74 | 75 |
Administrative expenses | 2 | (1) |  | 0 | (4) |
Underwriting income (loss) | 87 | 91 |  | 222 | 209 |
Net investment income (loss) | 7 | 6 |  | 20 | 18 |
Other (income) expense | 0 | 0 |  | 1 | 1 |
Amortization of purchased intangibles | 7 | 8 |  | 21 | 22 |
Segment Income (loss) | 87 | 89 |  | 220 | 204 |
Overseas General Insurance [Member] |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Net premiums written | 2,081 | 1,966 | [1] | 6,664 | 6,185 | [2]
Net premiums earned | 2,157 | 2,064 |  | 6,425 | 6,018 |
Losses and loss expenses | 1,114 | 1,281 |  | 3,263 | 3,316 |
Policy benefits | 0 | 0 |  | 0 | 0 |
Policy acquisition costs | 582 | 569 |  | 1,754 | 1,653 |
Administrative expenses | 252 | 246 |  | 757 | 734 |
Underwriting income (loss) | 209 | (32) |  | 651 | 315 |
Net investment income (loss) | 155 | 164 |  | 461 | 460 |
Other (income) expense | (7) | (10) |  | (12) | (14) |
Amortization of purchased intangibles | 8 | 11 |  | 29 | 33 |
Segment Income (loss) | 363 | 131 |  | 1,095 | 756 |
Global Reinsurance [Member] |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Net premiums written | 164 | 191 |  | 554 | 580 |
Net premiums earned | 157 | 185 |  | 492 | 542 |
Losses and loss expenses | 86 | 295 |  | 236 | 435 |
Policy benefits | 0 | 0 |  | 0 | 0 |
Policy acquisition costs | 40 | 43 |  | 120 | 137 |
Administrative expenses | 10 | 11 |  | 29 | 33 |
Underwriting income (loss) | 21 | (164) |  | 107 | (63) |
Net investment income (loss) | 63 | 80 |  | 192 | 207 |
Other (income) expense | (13) | (3) |  | (26) | (2) |
Amortization of purchased intangibles | 0 | 0 |  | 0 | 0 |
Segment Income (loss) | 97 | (81) |  | 325 | 146 |
Life Insurance [Member] |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Net premiums written | 564 | 539 |  | 1,688 | 1,586 |
Net premiums earned | 551 | 527 |  | 1,643 | 1,548 |
Losses and loss expenses | 195 | 181 |  | 584 | 556 |
Policy benefits | 127 | 169 |  | 428 | 500 |
Policy acquisition costs | 139 | 132 |  | 405 | 376 |
Administrative expenses | 77 | 77 |  | 235 | 226 |
Underwriting income (loss) | 13 | (32) |  | (9) | (110) |
Net investment income (loss) | 85 | 78 |  | 253 | 230 |
Other (income) expense | 20 | (19) |  | 24 | (60) |
Amortization of purchased intangibles | 0 | 1 |  | 1 | 2 |
Segment Income (loss) | 78 | 64 |  | 219 | 178 |
Corporate Segment [Member] |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Net premiums written | 0 | 0 |  | 0 | 0 |
Net premiums earned | 0 | 0 |  | 0 | 0 |
Losses and loss expenses | 13 | 89 |  | 72 | 145 |
Policy benefits | 0 | 0 |  | 0 | 0 |
Policy acquisition costs | 0 | 0 |  | 0 | 0 |
Administrative expenses | 58 | 64 |  | 200 | 187 |
Underwriting income (loss) | (71) | (153) |  | (272) | (332) |
Net investment income (loss) | (49) | (69) |  | (162) | (220) |
Other (income) expense | (144) | (83) |  | (275) | (257) |
Amortization of purchased intangibles | 64 | 41 |  | 192 | 125 |
Segment Income (loss) | (40) | (180) |  | (351) | (420) |
Net realized gains (losses) including OTTI | 19 | (10) |  | 35 | 84 |
Interest expense | 164 | 150 |  | 488 | 451 |
Chubb integration expenses | 16 | 50 |  | 39 | 233 |
Income tax expense | 183 | (85) |  | 536 | 243 |
Net income (loss) | $ (384) | $ (305) |  | $ (1,379) | $ (1,263) |
[1] | The 2017 net premiums written amount was revised to reflect the transfer of certain multinational accounts ($3 million) from the North America Commercial P&C Insurance segment to the Overseas General Insurance segment to better align the reporting with the management of these businesses in 2018. There is no impact on a consolidated basis.
[2] | The 2017 net premiums written amount was revised to reflect the transfer of certain multinational accounts ($16 million) from the North America Commercial P&C Insurance segment to the Overseas General Insurance segment to better align the reporting with the management of these businesses in 2018. There is no impact on a consolidated basis.

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