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Investments (Gross Unrealized Losses Related To Available-For-Sale And Held-To-Maturity Investments) (Detail) - USD ($) $ in Millions | Dec. 31, 2016 | Dec. 31, 2015
--- | --- | ---
Available For Sale Securities [Abstract] |  |
Less than 12 months, fair value | $ 1,872 | $ 2,389
Less than 12 months, unrealized losses | (62) | (36)
12 months or longer, fair value | 300 | 413
12 months or longer, unrealized losses | (86) | (136)
Total available-for-sale, fair value | 2,172 | 2,802
Total available-for-sale, unrealized losses | (148) | (172)
Variable Interest Entity Primary Beneficiary [Member] |  |
Held To Maturity Securities [Abstract] |  |
Less than 12 months, fair value | 0 | 1,093
Less than 12 months, unrealized losses | 0 | (17)
12 months or longer, fair value | 876 | 280
12 months or longer, unrealized losses | (14) | (295)
Total held-to-maturity, fair value | 876 | 1,373
Total held-to-maturity, unrealized losses | (14) | (312)
Corporate Obligations [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |
Held To Maturity Securities [Abstract] |  |
Less than 12 months, fair value | 0 | 1,093
Less than 12 months, unrealized losses | 0 | (17)
12 months or longer, fair value | 876 | 280
12 months or longer, unrealized losses | (14) | (295)
Total held-to-maturity, fair value | 876 | 1,373
Total held-to-maturity, unrealized losses | (14) | (312)
Perpetual Debt And Equity Securities [Member] |  |
Available For Sale Securities [Abstract] |  |
Less than 12 months, fair value | 0 | 2
Less than 12 months, unrealized losses | 0 | 0
12 months or longer, fair value | 0 | 3
12 months or longer, unrealized losses | 0 | 0
Total available-for-sale, fair value | 0 | 5
Total available-for-sale, unrealized losses | 0 | 0
Fixed Maturities [Member] |  |
Available For Sale Securities [Abstract] |  |
Less than 12 months, fair value | 1,872 | 2,387
Less than 12 months, unrealized losses | (62) | (36)
12 months or longer, fair value | 300 | 410
12 months or longer, unrealized losses | (86) | (136)
Total available-for-sale, fair value | 2,172 | 2,797
Total available-for-sale, unrealized losses | (148) | (172)
Fixed Maturities [Member] | U S Treasury And Government [Member] |  |
Available For Sale Securities [Abstract] |  |
Less than 12 months, fair value | 432 | 434
Less than 12 months, unrealized losses | (10) | (2)
12 months or longer, fair value | 0 | 50
12 months or longer, unrealized losses | 0 | (1)
Total available-for-sale, fair value | 432 | 484
Total available-for-sale, unrealized losses | (10) | (3)
Fixed Maturities [Member] | US States And Political Subdivisions [Member] |  |
Available For Sale Securities [Abstract] |  |
Less than 12 months, fair value | 339 | 536
Less than 12 months, unrealized losses | (13) | (11)
12 months or longer, fair value | 18 | 42
12 months or longer, unrealized losses | (2) | (3)
Total available-for-sale, fair value | 357 | 578
Total available-for-sale, unrealized losses | (15) | (14)
Fixed Maturities [Member] | Foreign Government Debt [Member] |  |
Available For Sale Securities [Abstract] |  |
Less than 12 months, fair value | 5 | 32
Less than 12 months, unrealized losses | 0 | (2)
12 months or longer, fair value | 0 | 0
12 months or longer, unrealized losses | 0 | 0
Total available-for-sale, fair value | 5 | 32
Total available-for-sale, unrealized losses | 0 | (2)
Fixed Maturities [Member] | Corporate Obligations [Member] |  |
Available For Sale Securities [Abstract] |  |
Less than 12 months, fair value | 534 | 693
Less than 12 months, unrealized losses | (29) | (14)
12 months or longer, fair value | 52 | 78
12 months or longer, unrealized losses | (73) | (89)
Total available-for-sale, fair value | 586 | 771
Total available-for-sale, unrealized losses | (102) | (103)
Fixed Maturities [Member] | Residential Mortgage Backed Agency [Member] |  |
Available For Sale Securities [Abstract] |  |
Less than 12 months, fair value | 436 | 399
Less than 12 months, unrealized losses | (9) | (4)
12 months or longer, fair value | 122 | 159
12 months or longer, unrealized losses | (3) | (5)
Total available-for-sale, fair value | 558 | 558
Total available-for-sale, unrealized losses | (12) | (9)
Fixed Maturities [Member] | Residential Mortgage Backed Non Agency [Member] |  |
Available For Sale Securities [Abstract] |  |
Less than 12 months, fair value | 1 | 24
Less than 12 months, unrealized losses | 0 | (2)
12 months or longer, fair value | 29 | 17
12 months or longer, unrealized losses | (6) | (4)
Total available-for-sale, fair value | 30 | 41
Total available-for-sale, unrealized losses | (6) | (6)
Fixed Maturities [Member] | Commercial Mortgage Backed Securities [Member] |  |
Available For Sale Securities [Abstract] |  |
Less than 12 months, fair value | 6 | 25
Less than 12 months, unrealized losses | 0 | 0
12 months or longer, fair value | 15 | 1
12 months or longer, unrealized losses | 0 | 0
Total available-for-sale, fair value | 21 | 26
Total available-for-sale, unrealized losses | 0 | 0
Fixed Maturities [Member] | Collateralized Debt Obligations [Member] |  |
Available For Sale Securities [Abstract] |  |
Less than 12 months, fair value | 7 | 2
Less than 12 months, unrealized losses | 0 | 0
12 months or longer, fair value | 15 | 29
12 months or longer, unrealized losses | 0 | (18)
Total available-for-sale, fair value | 22 | 31
Total available-for-sale, unrealized losses | 0 | (18)
Fixed Maturities [Member] | Other Asset Backed [Member] |  |
Available For Sale Securities [Abstract] |  |
Less than 12 months, fair value | 112 | 242
Less than 12 months, unrealized losses | (1) | (1)
12 months or longer, fair value | 49 | 34
12 months or longer, unrealized losses | (2) | (16)
Total available-for-sale, fair value | 161 | 276
Total available-for-sale, unrealized losses | $ (3) | $ (17)

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