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Segment Information (Operations By Segment) (Detail) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Net premiums written |  |  |  |  |  |  |  |  |  | $ 32,275 | $ 30,579 | $ 29,244
Net premiums earned |  | $ 7,935 | $ 8,327 | $ 7,891 | $ 7,137 | $ 7,465 | $ 7,908 | $ 7,664 | $ 7,027 | 31,290 | 30,064 | 29,034
Losses and loss expenses |  | 4,865 | 5,052 | 4,715 | 4,098 | 4,610 | 4,868 | 4,487 | 4,102 | 18,730 | 18,067 | 18,454
Policy benefits |  | 225 | 158 | 161 | 196 | 162 | 127 | 150 | 151 | 740 | 590 | 676
Policy Acquisition Costs |  |  |  |  |  |  |  |  |  | 6,153 | 5,912 | 5,781
Administrative expenses |  |  |  |  |  |  |  |  |  | 3,030 | 2,886 | 2,833
Underwriting income (loss) |  |  |  |  |  |  |  |  |  | 2,637 | 2,609 | 1,290
Net Investment Income |  | 858 | 873 | 859 | 836 | 848 | 823 | 828 | 806 | 3,426 | 3,305 | 3,125
Other (Income) Expense |  |  |  |  |  |  |  |  |  | (596) | (434) | (400)
Amortization of Purchased Intangibles |  |  |  |  |  |  |  |  |  | 305 | 339 | 260
Segment Underwriting Income Loss and Net Investment Income Loss |  |  |  |  |  |  |  |  |  | 6,354 | 6,009 | 4,555
Interest expense |  |  |  |  |  |  |  |  |  | 552 | 641 | 607
Chubb integration expenses |  |  |  |  |  |  |  |  |  | 23 | 59 | 310
Income tax expense (benefit) |  |  |  |  |  |  |  |  |  | 795 | 695 | (139)
Net income |  | 1,173 | 1,091 | 1,150 | 1,040 | 355 | 1,231 | 1,294 | 1,082 | 4,454 | 3,962 | 3,861
Derivative, Gain (Loss) on Derivative, Net |  |  |  |  |  |  |  |  |  | 585 | 330 | (87)
Other (income) expense |  |  |  |  |  |  |  |  |  | (596) | (434) | (400)
(Gains) losses from fair value changes in separate account assets | [1] |  |  |  |  |  |  |  |  | 44 | (38) | 97
Net Realized Gains Losses |  | $ (55) | $ (155) | $ (223) | $ (97) | $ (687) | $ 19 | $ 18 | $ (2) | (530) | (652) | 84
North America Commercial P&C Insurance |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Net premiums written |  |  |  |  |  |  |  |  |  | 13,375 | 12,485 | 12,019
Net premiums earned |  |  |  |  |  |  |  |  |  | 12,922 | 12,402 | 12,191
Losses and loss expenses |  |  |  |  |  |  |  |  |  | 8,206 | 8,000 | 8,287
Policy benefits |  |  |  |  |  |  |  |  |  | 0 | 0 | 0
Policy Acquisition Costs |  |  |  |  |  |  |  |  |  | 1,831 | 1,829 | 1,873
Administrative expenses |  |  |  |  |  |  |  |  |  | 1,028 | 966 | 981
Underwriting income (loss) |  |  |  |  |  |  |  |  |  | 1,857 | 1,607 | 1,050
Net Investment Income |  |  |  |  |  |  |  |  |  | 2,082 | 2,033 | 1,961
Other (Income) Expense |  |  |  |  |  |  |  |  |  | (3) | (25) | 1
Amortization of Purchased Intangibles |  |  |  |  |  |  |  |  |  | 0 | 0 | 0
Segment Underwriting Income Loss and Net Investment Income Loss |  |  |  |  |  |  |  |  |  | 3,942 | 3,665 | 3,010
Segment Insurance North American Personal P&C [Member] [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Net premiums written |  |  |  |  |  |  |  |  |  | 4,787 | 4,674 | 4,533
Net premiums earned |  |  |  |  |  |  |  |  |  | 4,694 | 4,593 | 4,399
Losses and loss expenses |  |  |  |  |  |  |  |  |  | 3,043 | 3,229 | 3,265
Policy benefits |  |  |  |  |  |  |  |  |  | 0 | 0 | 0
Policy Acquisition Costs |  |  |  |  |  |  |  |  |  | 948 | 939 | 899
Administrative expenses |  |  |  |  |  |  |  |  |  | 286 | 269 | 264
Underwriting income (loss) |  |  |  |  |  |  |  |  |  | 417 | 156 | (29)
Net Investment Income |  |  |  |  |  |  |  |  |  | 258 | 236 | 226
Other (Income) Expense |  |  |  |  |  |  |  |  |  | 3 | 1 | 4
Amortization of Purchased Intangibles |  |  |  |  |  |  |  |  |  | 12 | 13 | 16
Segment Underwriting Income Loss and Net Investment Income Loss |  |  |  |  |  |  |  |  |  | 660 | 378 | 177
North America Agricultural Insurance |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Net premiums written |  |  |  |  |  |  |  |  |  | 1,810 | 1,577 | 1,516
Net premiums earned |  |  |  |  |  |  |  |  |  | 1,795 | 1,569 | 1,508
Losses and loss expenses |  |  |  |  |  |  |  |  |  | 1,608 | 1,111 | 1,036
Policy benefits |  |  |  |  |  |  |  |  |  | 0 | 0 | 0
Policy Acquisition Costs |  |  |  |  |  |  |  |  |  | 84 | 79 | 81
Administrative expenses |  |  |  |  |  |  |  |  |  | 6 | (9) | (8)
Underwriting income (loss) |  |  |  |  |  |  |  |  |  | 97 | 388 | 399
Net Investment Income |  |  |  |  |  |  |  |  |  | 30 | 28 | 25
Other (Income) Expense |  |  |  |  |  |  |  |  |  | 1 | 2 | 2
Amortization of Purchased Intangibles |  |  |  |  |  |  |  |  |  | 28 | 28 | 29
Segment Underwriting Income Loss and Net Investment Income Loss |  |  |  |  |  |  |  |  |  | 98 | 386 | 393
Segment Income Loss Including Gains Losses On Crop Derivatives |  |  |  |  |  |  |  |  |  | 89 |  |
Derivative, Gain (Loss) on Derivative, Net |  |  |  |  |  |  |  |  |  | 8 |  |
Overseas General Insurance |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Net premiums written |  |  |  |  |  |  |  |  |  | 9,262 | 8,902 | 8,350
Net premiums earned |  |  |  |  |  |  |  |  |  | 8,882 | 8,612 | 8,131
Losses and loss expenses |  |  |  |  |  |  |  |  |  | 4,606 | 4,429 | 4,281
Policy benefits |  |  |  |  |  |  |  |  |  | 0 | 0 | 0
Policy Acquisition Costs |  |  |  |  |  |  |  |  |  | 2,501 | 2,346 | 2,221
Administrative expenses |  |  |  |  |  |  |  |  |  | 1,033 | 1,014 | 982
Underwriting income (loss) |  |  |  |  |  |  |  |  |  | 742 | 823 | 647
Net Investment Income |  |  |  |  |  |  |  |  |  | 588 | 619 | 610
Other (Income) Expense |  |  |  |  |  |  |  |  |  | 12 | 0 | (4)
Amortization of Purchased Intangibles |  |  |  |  |  |  |  |  |  | 45 | 41 | 45
Segment Underwriting Income Loss and Net Investment Income Loss |  |  |  |  |  |  |  |  |  | 1,273 | 1,401 | 1,216
Segment Global Reinsurance [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Net premiums written |  |  |  |  |  |  |  |  |  | 649 | 671 | 685
Net premiums earned |  |  |  |  |  |  |  |  |  | 654 | 670 | 704
Losses and loss expenses |  |  |  |  |  |  |  |  |  | 352 | 479 | 561
Policy benefits |  |  |  |  |  |  |  |  |  | 0 | 0 | 0
Policy Acquisition Costs |  |  |  |  |  |  |  |  |  | 169 | 162 | 177
Administrative expenses |  |  |  |  |  |  |  |  |  | 35 | 41 | 44
Underwriting income (loss) |  |  |  |  |  |  |  |  |  | 98 | (12) | (78)
Net Investment Income |  |  |  |  |  |  |  |  |  | 220 | 257 | 273
Other (Income) Expense |  |  |  |  |  |  |  |  |  | (58) | (32) | (1)
Amortization of Purchased Intangibles |  |  |  |  |  |  |  |  |  | 0 | 0 | 0
Segment Underwriting Income Loss and Net Investment Income Loss |  |  |  |  |  |  |  |  |  | 376 | 277 | 196
Life Insurance |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Net premiums written |  |  |  |  |  |  |  |  |  | 2,392 | 2,270 | 2,141
Net premiums earned |  |  |  |  |  |  |  |  |  | 2,343 | 2,218 | 2,101
Losses and loss expenses |  |  |  |  |  |  |  |  |  | 757 | 766 | 739
Policy benefits |  |  |  |  |  |  |  |  |  | 740 | 590 | 676
Policy Acquisition Costs |  |  |  |  |  |  |  |  |  | 620 | 557 | 530
Administrative expenses |  |  |  |  |  |  |  |  |  | 323 | 310 | 303
Underwriting income (loss) |  |  |  |  |  |  |  |  |  | (97) | (5) | (147)
Net Investment Income |  |  |  |  |  |  |  |  |  | 373 | 341 | 313
Other (Income) Expense |  |  |  |  |  |  |  |  |  | (92) | 26 | (84)
Amortization of Purchased Intangibles |  |  |  |  |  |  |  |  |  | 2 | 2 | 2
Segment Underwriting Income Loss and Net Investment Income Loss |  |  |  |  |  |  |  |  |  | 366 | 308 | 248
Management underwriting income loss Insurance |  |  |  |  |  |  |  |  |  | 320 |  |
(Gains) losses from fair value changes in separate account assets |  |  |  |  |  |  |  |  |  | (44) |  |
Corporate and Other |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Net premiums written |  |  |  |  |  |  |  |  |  | 0 | 0 | 0
Net premiums earned |  |  |  |  |  |  |  |  |  | 0 | 0 | 0
Losses and loss expenses |  |  |  |  |  |  |  |  |  | 158 | 53 | 285
Policy benefits |  |  |  |  |  |  |  |  |  | 0 | 0 | 0
Policy Acquisition Costs |  |  |  |  |  |  |  |  |  | 0 | 0 | 0
Administrative expenses |  |  |  |  |  |  |  |  |  | 319 | 295 | 267
Underwriting income (loss) |  |  |  |  |  |  |  |  |  | (477) | (348) | (552)
Net Investment Income |  |  |  |  |  |  |  |  |  | (125) | (209) | (283)
Other (Income) Expense |  |  |  |  |  |  |  |  |  | (459) | (406) | (318)
Amortization of Purchased Intangibles |  |  |  |  |  |  |  |  |  | 218 | 255 | 168
Segment Underwriting Income Loss and Net Investment Income Loss |  |  |  |  |  |  |  |  |  | (361) | (406) | (685)
Interest expense |  |  |  |  |  |  |  |  |  | 552 | 641 | 607
Chubb integration expenses |  |  |  |  |  |  |  |  |  | 23 | 59 | 310
Income tax expense (benefit) |  |  |  |  |  |  |  |  |  | 795 | 695 | (139)
Net income |  |  |  |  |  |  |  |  |  | (2,261) | (2,453) | (1,379)
Net Realized Gains Losses |  |  |  |  |  |  |  |  |  | $ (530) | $ (652) | $ 84
[1] | Related to gains (losses) from fair value changes in separate account assets that do not qualify for separate account reporting under GAAP.

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