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Investments (Gross Unrealized Losses Related To Available-For-Sale And Held-To-Maturity Investments) (Detail) - USD ($) $ in Millions | Sep. 30, 2018 | Dec. 31, 2017
--- | --- | ---
Available For Sale Securities [Abstract] |  |
Less than 12 months, fair value | $ 1,955 |
Less than 12 months, unrealized losses | (51) |
12 months or longer, fair value | 700 |
12 months or longer, unrealized losses | (117) |
Total available-for-sale, fair value | 2,655 |
Total available-for-sale, unrealized losses | (168) |
Variable Interest Entity Primary Beneficiary [Member] |  |
Held To Maturity Securities [Abstract] |  |
Less than 12 months, fair value | 313 |
Less than 12 months, unrealized losses | (2) |
12 months or longer, fair value | 0 |
12 months or longer, unrealized losses | 0 |
Total held-to-maturity, fair value | 313 |
Total held-to-maturity, unrealized losses | (2) |
Corporate Obligations [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |
Held To Maturity Securities [Abstract] |  |
Less than 12 months, fair value | 313 |
Less than 12 months, unrealized losses | (2) |
12 months or longer, fair value | 0 |
12 months or longer, unrealized losses | 0 |
Total held-to-maturity, fair value | 313 |
Total held-to-maturity, unrealized losses | (2) |
Fixed Maturities [Member] |  |
Available For Sale Securities [Abstract] |  |
Less than 12 months, fair value | 1,955 | $ 1,204
Less than 12 months, unrealized losses | (51) | (13)
12 months or longer, fair value | 700 | 617
12 months or longer, unrealized losses | (117) | (93)
Total available-for-sale, fair value | 2,655 | 1,821
Total available-for-sale, unrealized losses | (168) | (106)
Fixed Maturities [Member] | U S Treasury And Government [Member] |  |
Available For Sale Securities [Abstract] |  |
Less than 12 months, fair value | 396 | 353
Less than 12 months, unrealized losses | (7) | (1)
12 months or longer, fair value | 206 | 124
12 months or longer, unrealized losses | (12) | (5)
Total available-for-sale, fair value | 602 | 477
Total available-for-sale, unrealized losses | (19) | (6)
Fixed Maturities [Member] | US States And Political Subdivisions [Member] |  |
Available For Sale Securities [Abstract] |  |
Less than 12 months, fair value | 92 | 203
Less than 12 months, unrealized losses | (3) | (8)
12 months or longer, fair value | 123 | 116
12 months or longer, unrealized losses | (11) | (4)
Total available-for-sale, fair value | 215 | 319
Total available-for-sale, unrealized losses | (14) | (12)
Fixed Maturities [Member] | Foreign Government Debt [Member] |  |
Available For Sale Securities [Abstract] |  |
Less than 12 months, fair value | 9 | 8
Less than 12 months, unrealized losses | 0 | 0
12 months or longer, fair value | 0 | 0
12 months or longer, unrealized losses | 0 | 0
Total available-for-sale, fair value | 9 | 8
Total available-for-sale, unrealized losses | 0 | 0
Fixed Maturities [Member] | Corporate Obligations [Member] |  |
Available For Sale Securities [Abstract] |  |
Less than 12 months, fair value | 1,116 | 425
Less than 12 months, unrealized losses | (38) | (3)
12 months or longer, fair value | 213 | 163
12 months or longer, unrealized losses | (84) | (77)
Total available-for-sale, fair value | 1,329 | 588
Total available-for-sale, unrealized losses | (122) | (80)
Fixed Maturities [Member] | Residential Mortgage Backed Agency [Member] |  |
Available For Sale Securities [Abstract] |  |
Less than 12 months, fair value | 119 | 105
Less than 12 months, unrealized losses | (2) | (1)
12 months or longer, fair value | 95 | 156
12 months or longer, unrealized losses | (5) | (3)
Total available-for-sale, fair value | 214 | 261
Total available-for-sale, unrealized losses | (7) | (4)
Fixed Maturities [Member] | Residential Mortgage Backed Non Agency [Member] |  |
Available For Sale Securities [Abstract] |  |
Less than 12 months, fair value | 0 | 0
Less than 12 months, unrealized losses | 0 | 0
12 months or longer, fair value | 14 | 14
12 months or longer, unrealized losses | (3) | (4)
Total available-for-sale, fair value | 14 | 14
Total available-for-sale, unrealized losses | (3) | (4)
Fixed Maturities [Member] | Commercial Mortgage Backed Securities [Member] |  |
Available For Sale Securities [Abstract] |  |
Less than 12 months, fair value | 29 | 27
Less than 12 months, unrealized losses | 0 | 0
12 months or longer, fair value | 19 | 5
12 months or longer, unrealized losses | (2) | 0
Total available-for-sale, fair value | 48 | 32
Total available-for-sale, unrealized losses | (2) | 0
Fixed Maturities [Member] | Collateralized Debt Obligations [Member] |  |
Available For Sale Securities [Abstract] |  |
Less than 12 months, fair value | 73 | 12
Less than 12 months, unrealized losses | 0 | 0
12 months or longer, fair value | 0 | 0
12 months or longer, unrealized losses | 0 | 0
Total available-for-sale, fair value | 73 | 12
Total available-for-sale, unrealized losses | 0 | 0
Fixed Maturities [Member] | Other Asset Backed [Member] |  |
Available For Sale Securities [Abstract] |  |
Less than 12 months, fair value | 121 | 71
Less than 12 months, unrealized losses | (1) | 0
12 months or longer, fair value | 30 | 39
12 months or longer, unrealized losses | 0 | 0
Total available-for-sale, fair value | 151 | 110
Total available-for-sale, unrealized losses | $ (1) | $ 0

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