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Investments (Amortized Cost And Fair Value Of Available-For-Sale and Held-To-Maturity Investment Portfolios) (Detail) - USD ($) $ in Millions | Dec. 31, 2016 | Dec. 31, 2015
--- | --- | ---
Available For Sale Securities [Abstract] |  |  |
Amortized cost |  | $ 5,450 | $ 6,160
Gross unrealized gains |  | 129 | 132
Gross unrealized losses |  | (148) | (172)
Total available-for-sale, fair value |  | 5,431 | 6,120
Other-than-temporary impairments | [1] | (75) | (89)
Variable Interest Entity Primary Beneficiary [Member] |  |  |
Held To Maturity Securities [Abstract] |  |  |
Amortized cost |  | 890 | 2,689
Gross unrealized gains |  | 0 | 24
Gross unrealized losses |  | (14) | (312)
Total Held-To-Maturity, fair value |  | 876 | 2,401
Other-Than-Temporary Impairments | [1] | 0 | 0
Corporate Obligations [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |
Held To Maturity Securities [Abstract] |  |  |
Amortized cost |  | 890 | 2,689
Gross unrealized gains |  | 0 | 24
Gross unrealized losses |  | (14) | (312)
Total Held-To-Maturity, fair value |  | 876 | 2,401
Other-Than-Temporary Impairments | [1] | 0 | 0
Money Market Securities [Member] |  |  |
Available For Sale Securities [Abstract] |  |  |
Amortized cost |  | 517 | 351
Gross unrealized gains |  | 0 | 0
Gross unrealized losses |  | 0 | 0
Total available-for-sale, fair value |  | 517 | 351
Other-than-temporary impairments | [1] | 0 | 0
Perpetual Debt And Equity Securities [Member] |  |  |
Available For Sale Securities [Abstract] |  |  |
Amortized cost |  | 4 | 12
Gross unrealized gains |  | 1 | 1
Gross unrealized losses |  | 0 | 0
Total available-for-sale, fair value |  | 5 | 13
Other-than-temporary impairments | [1] | 0 | 0
Fixed Maturities [Member] |  |  |
Available For Sale Securities [Abstract] |  |  |
Amortized cost |  | 4,929 | 5,797
Gross unrealized gains |  | 128 | 131
Gross unrealized losses |  | (148) | (172)
Total available-for-sale, fair value |  | 4,909 | 5,756
Other-than-temporary impairments | [1] | (75) | (89)
Fixed Maturities [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |
Held To Maturity Securities [Abstract] |  |  |
Amortized cost |  | 890 |
Total Held-To-Maturity, fair value |  | 876 |
Fixed Maturities [Member] | U S Treasury And Government [Member] |  |  |
Available For Sale Securities [Abstract] |  |  |
Amortized cost |  | 909 | 947
Gross unrealized gains |  | 30 | 32
Gross unrealized losses |  | (10) | (3)
Total available-for-sale, fair value |  | 929 | 976
Other-than-temporary impairments | [1] | 0 | 0
Fixed Maturities [Member] | US States And Political Subdivisions [Member] |  |  |
Available For Sale Securities [Abstract] |  |  |
Amortized cost |  | 1,382 | 1,674
Gross unrealized gains |  | 72 | 65
Gross unrealized losses |  | (15) | (14)
Total available-for-sale, fair value |  | 1,439 | 1,725
Other-than-temporary impairments | [1] | 0 | 0
Fixed Maturities [Member] | Foreign Governments [Member] |  |  |
Available For Sale Securities [Abstract] |  |  |
Amortized cost |  | 8 | 197
Gross unrealized gains |  | 0 | 3
Gross unrealized losses |  | 0 | (2)
Total available-for-sale, fair value |  | 8 | 198
Other-than-temporary impairments | [1] | 0 | 0
Fixed Maturities [Member] | Corporate Obligations [Member] |  |  |
Available For Sale Securities [Abstract] |  |  |
Amortized cost |  | 1,352 | 1,516
Gross unrealized gains |  | 20 | 21
Gross unrealized losses |  | (102) | (103)
Total available-for-sale, fair value |  | 1,270 | 1,434
Other-than-temporary impairments | [1] | (73) | (85)
Fixed Maturities [Member] | Residential Mortgage-Backed Agency [Member] |  |  |
Available For Sale Securities [Abstract] |  |  |
Amortized cost |  | 871 | 995
Gross unrealized gains |  | 3 | 7
Gross unrealized losses |  | (12) | (9)
Total available-for-sale, fair value |  | 862 | 993
Other-than-temporary impairments | [1] | 0 | 0
Fixed Maturities [Member] | Residential Mortgage-Backed Non-Agency [Member] |  |  |
Available For Sale Securities [Abstract] |  |  |
Amortized cost |  | 50 | 55
Gross unrealized gains |  | 1 | 2
Gross unrealized losses |  | (6) | (6)
Total available-for-sale, fair value |  | 45 | 51
Other-than-temporary impairments | [1] | (3) | (4)
Fixed Maturities [Member] | Commercial Mortgage-Backed [Member] |  |  |
Available For Sale Securities [Abstract] |  |  |
Amortized cost |  | 41 | 31
Gross unrealized gains |  | 0 | 0
Gross unrealized losses |  | 0 | 0
Total available-for-sale, fair value |  | 41 | 31
Other-than-temporary impairments | [1] | 0 | 0
Fixed Maturities [Member] | Collateralized Debt Obligations [Member] |  |  |
Available For Sale Securities [Abstract] |  |  |
Amortized cost |  | 22 | 51
Gross unrealized gains |  | 0 | 0
Gross unrealized losses |  | 0 | (18)
Total available-for-sale, fair value |  | 22 | 33
Other-than-temporary impairments | [1] | 0 | 0
Fixed Maturities [Member] | Other Asset-Backed [Member] |  |  |
Available For Sale Securities [Abstract] |  |  |
Amortized cost |  | 294 | 331
Gross unrealized gains |  | 2 | 1
Gross unrealized losses |  | (3) | (17)
Total available-for-sale, fair value |  | 293 | 315
Other-than-temporary impairments | [1] | $ 1 | $ 0
[1] | Represents unrealized gains or losses on other than temporarily impaired securities recognized in AOCI, which includes the non-credit component of impairments, as well as all subsequent changes in fair value of such impaired securities reported in AOCI.

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