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Segment Information (Operations By Segment) (Detail) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2017 | Sep. 30, 2016 | Sep. 30, 2017 | Sep. 30, 2016
Segment Reporting Information [Line Items] |  |  |  |
Net premiums written | $ 7,902 | $ 7,573 | $ 22,193 | $ 21,207
Net premiums earned | 7,807 | 7,688 | 21,816 | 21,690
Losses and loss expenses | 6,247 | 4,269 | 14,182 | 12,197
Policy benefits | 169 | 155 | 500 | 427
Policy acquisition costs | 1,488 | 1,514 | 4,334 | 4,487
Administrative expenses | 714 | 772 | 2,096 | 2,373
Underwriting income (loss) | (811) | 978 | 704 | 2,206
Net investment income | 813 | 739 | 2,328 | 2,121
Other (income) expense | (118) | (91) | (333) | (92)
Amortization of purchased intangibles | 65 | 4 | 194 | 16
Segment Income (loss) | 55 | 1,804 | 3,171 | 4,403
Net realized gains (losses) including OTTI | (10) | 100 | 84 | (510)
Interest expense | 150 | 152 | 451 | 451
Chubb integration expenses | 50 | 115 | 233 | 361
Income tax benefit | (85) | 277 | 243 | 556
Net income (loss) | (70) | 1,360 | 2,328 | 2,525
North America Commercial P&C Insurance [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Net premiums written | 3,089 | 3,110 | 9,035 | 8,657
Net premiums earned | 3,016 | 3,086 | 9,156 | 9,130
Losses and loss expenses | 2,580 | 1,863 | 6,376 | 5,581
Policy benefits | 0 |  | 0 | 0
Policy acquisition costs | 469 | 522 | 1,420 | 1,549
Administrative expenses | 256 | 275 | 728 | 840
Underwriting income (loss) | (289) | 426 | 632 | 1,160
Net investment income | 497 | 477 | 1,465 | 1,371
Other (income) expense | (4) | 3 | (4) | (6)
Amortization of purchased intangibles | 0 | 0 | 0 | 0
Segment Income (loss) | 212 | 900 | 2,101 | 2,537
North America Personal P&C Insurance [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Net premiums written | 1,194 | 1,011 | 3,433 | 3,113
Net premiums earned | 1,117 | 1,081 | 3,296 | 3,245
Losses and loss expenses | 1,062 | 594 | 2,378 | 1,916
Policy benefits | 0 |  | 0 | 0
Policy acquisition costs | 226 | 229 | 673 | 747
Administrative expenses | 61 | 89 | 192 | 275
Underwriting income (loss) | (232) | 169 | 53 | 307
Net investment income | 57 | 53 | 168 | 155
Other (income) expense | 1 | 2 | 3 | 6
Amortization of purchased intangibles | 4 | 4 | 12 | 16
Segment Income (loss) | (180) | 216 | 206 | 440
North America Agricultural Insurance [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Net premiums written | 926 | 849 | 1,390 | 1,288
Net premiums earned | 898 | 819 | 1,256 | 1,169
Losses and loss expenses | 759 | 683 | 976 | 937
Policy benefits | 0 |  | 0 | 0
Policy acquisition costs | 49 | 48 | 75 | 77
Administrative expenses | (1) | 1 | (4) | (1)
Underwriting income (loss) | 91 | 87 | 209 | 156
Net investment income | 6 | 5 | 18 | 15
Other (income) expense | 0 | 0 | 1 | 0
Amortization of purchased intangibles | 8 | 7 | 22 | 22
Segment Income (loss) | 89 | 85 | 204 | 149
Overseas General Insurance [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Net premiums written | 1,963 | 1,940 | 6,169 | 6,012
Net premiums earned | 2,064 | 2,034 | 6,018 | 6,082
Losses and loss expenses | 1,281 | 843 | 3,316 | 2,953
Policy benefits | 0 |  | 0 | 0
Policy acquisition costs | 569 | 546 | 1,653 | 1,586
Administrative expenses | 246 | 261 | 734 | 801
Underwriting income (loss) | (32) | 384 | 315 | 742
Net investment income | 164 | 152 | 460 | 445
Other (income) expense | (10) | (6) | (14) | (16)
Amortization of purchased intangibles | 11 | 12 | 33 | 36
Segment Income (loss) | 131 | 530 | 756 | 1,167
Global Reinsurance [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Net premiums written | 191 | 131 | 580 | 562
Net premiums earned | 185 | 156 | 542 | 543
Losses and loss expenses | 295 | 49 | 435 | 225
Policy benefits | 0 |  | 0 | 0
Policy acquisition costs | 43 | 42 | 137 | 142
Administrative expenses | 11 | 12 | 33 | 40
Underwriting income (loss) | (164) | 53 | (63) | 136
Net investment income | 80 | 67 | 207 | 199
Other (income) expense | (3) | 0 | (2) | (3)
Amortization of purchased intangibles | 0 | 0 | 0 | 0
Segment Income (loss) | (81) | 120 | 146 | 338
Life Insurance [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Net premiums written | 539 | 532 | 1,586 | 1,575
Net premiums earned | 527 | 512 | 1,548 | 1,521
Losses and loss expenses | 181 | 174 | 556 | 498
Policy benefits | 169 | 155 | 500 | 427
Policy acquisition costs | 132 | 127 | 376 | 386
Administrative expenses | 77 | 77 | 226 | 226
Underwriting income (loss) | (32) | (21) | (110) | (16)
Net investment income | 78 | 71 | 230 | 207
Other (income) expense | (19) | (20) | (60) | (14)
Amortization of purchased intangibles | 1 | 1 | 2 | 2
Segment Income (loss) | 64 | 69 | 178 | 203
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 | 89 | 63 | 145 | 87
Policy benefits | 0 |  | 0 | 0
Policy acquisition costs | 0 | 0 | 0 | 0
Administrative expenses | 64 | 57 | 187 | 192
Underwriting income (loss) | (153) | (120) | (332) | (279)
Net investment income | (69) | (86) | (220) | (271)
Other (income) expense | (83) | (70) | (257) | (59)
Amortization of purchased intangibles | 41 | (20) | 125 | (60)
Segment Income (loss) | (180) | (116) | (420) | (431)
Net realized gains (losses) including OTTI | (10) | 100 | 84 | (510)
Interest expense | 150 | 152 | 451 | 451
Chubb integration expenses | 50 | 115 | 233 | 361
Income tax benefit | (85) | 277 | 243 | 556
Net income (loss) | $ (305) | $ (560) | $ (1,263) | $ (2,309)

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