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Investments (Gross Unrealized Losses Related To Available-For-Sale And Held-To-Maturity Investments) (Detail) - USD ($) $ in Millions | Dec. 31, 2015 | Dec. 31, 2014
--- | --- | ---
Available For Sale Securities [Abstract] |  |
Less than 12 months, fair value | $ 2,389 | $ 851
Less than 12 months, unrealized losses | (36) | (2)
12 months or longer, fair value | 413 | 1,220
12 months or longer, unrealized losses | (136) | (145)
Total available-for-sale, fair value | 2,802 | 2,071
Total available-for-sale, unrealized losses | (172) | (147)
Held To Maturity Securities [Abstract] |  |
Less than 12 months, fair value | 1,093 | 0
Less than 12 months, unrealized losses | (17) | 0
12 months or longer, fair value | 280 | 373
12 months or longer, unrealized losses | (295) | (202)
Total held-to-maturity, fair value | 1,373 | 373
Total held-to-maturity, unrealized losses | (312) | (202)
Corporate Obligations [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |
Held To Maturity Securities [Abstract] |  |
Less than 12 months, fair value | 1,093 | 0
Less than 12 months, unrealized losses | (17) | 0
12 months or longer, fair value | 280 | 373
12 months or longer, unrealized losses | (295) | (202)
Total held-to-maturity, fair value | 1,373 | 373
Total held-to-maturity, unrealized losses | (312) | (202)
Perpetual Debt And Equity Securities [Member] |  |
Available For Sale Securities [Abstract] |  |
Less than 12 months, fair value | 2 | 6
Less than 12 months, unrealized losses | 0 | 0
12 months or longer, fair value | 3 | 0
12 months or longer, unrealized losses | 0 | 0
Total available-for-sale, fair value | 5 | 6
Total available-for-sale, unrealized losses | 0 | 0
Fixed Maturities [Member] |  |
Available For Sale Securities [Abstract] |  |
Less than 12 months, fair value | 2,387 | 845
Less than 12 months, unrealized losses | (36) | (2)
12 months or longer, fair value | 410 | 1,220
12 months or longer, unrealized losses | (136) | (145)
Total available-for-sale, fair value | 2,797 | 2,065
Total available-for-sale, unrealized losses | (172) | (147)
Fixed Maturities [Member] | U S Treasury And Government [Member] |  |
Available For Sale Securities [Abstract] |  |
Less than 12 months, fair value | 434 | 197
Less than 12 months, unrealized losses | (2) | 0
12 months or longer, fair value | 50 | 175
12 months or longer, unrealized losses | (1) | (3)
Total available-for-sale, fair value | 484 | 372
Total available-for-sale, unrealized losses | (3) | (3)
Fixed Maturities [Member] | US States And Political Subdivisions [Member] |  |
Available For Sale Securities [Abstract] |  |
Less than 12 months, fair value | 536 | 60
Less than 12 months, unrealized losses | (11) | (1)
12 months or longer, fair value | 42 | 257
12 months or longer, unrealized losses | (3) | (7)
Total available-for-sale, fair value | 578 | 317
Total available-for-sale, unrealized losses | (14) | (8)
Fixed Maturities [Member] | Foreign Government Debt [Member] |  |
Available For Sale Securities [Abstract] |  |
Less than 12 months, fair value | 32 | 20
Less than 12 months, unrealized losses | (2) | 0
12 months or longer, fair value | 0 | 0
12 months or longer, unrealized losses | 0 | 0
Total available-for-sale, fair value | 32 | 20
Total available-for-sale, unrealized losses | (2) | 0
Fixed Maturities [Member] | Corporate Obligations [Member] |  |
Available For Sale Securities [Abstract] |  |
Less than 12 months, fair value | 693 | 468
Less than 12 months, unrealized losses | (14) | (1)
12 months or longer, fair value | 78 | 251
12 months or longer, unrealized losses | (89) | (91)
Total available-for-sale, fair value | 771 | 719
Total available-for-sale, unrealized losses | (103) | (92)
Fixed Maturities [Member] | Residential Mortgage Backed Agency [Member] |  |
Available For Sale Securities [Abstract] |  |
Less than 12 months, fair value | 399 | 16
Less than 12 months, unrealized losses | (4) | 0
12 months or longer, fair value | 159 | 387
12 months or longer, unrealized losses | (5) | (7)
Total available-for-sale, fair value | 558 | 403
Total available-for-sale, unrealized losses | (9) | (7)
Fixed Maturities [Member] | Residential Mortgage Backed Non Agency [Member] |  |
Available For Sale Securities [Abstract] |  |
Less than 12 months, fair value | 24 | 10
Less than 12 months, unrealized losses | (2) | 0
12 months or longer, fair value | 17 | 19
12 months or longer, unrealized losses | (4) | (4)
Total available-for-sale, fair value | 41 | 29
Total available-for-sale, unrealized losses | (6) | (4)
Fixed Maturities [Member] | Commercial Mortgage Backed Securities [Member] |  |
Available For Sale Securities [Abstract] |  |
Less than 12 months, fair value | 25 | 4
Less than 12 months, unrealized losses | 0 | 0
12 months or longer, fair value | 1 | 6
12 months or longer, unrealized losses | 0 | 0
Total available-for-sale, fair value | 26 | 10
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 | 2 | 1
Less than 12 months, unrealized losses | 0 | 0
12 months or longer, fair value | 29 | 81
12 months or longer, unrealized losses | (18) | (21)
Total available-for-sale, fair value | 31 | 82
Total available-for-sale, unrealized losses | (18) | (21)
Fixed Maturities [Member] | Other Asset Backed [Member] |  |
Available For Sale Securities [Abstract] |  |
Less than 12 months, fair value | 242 | 69
Less than 12 months, unrealized losses | (1) | 0
12 months or longer, fair value | 34 | 44
12 months or longer, unrealized losses | (16) | (12)
Total available-for-sale, fair value | 276 | 113
Total available-for-sale, unrealized losses | $ (17) | $ (12)

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