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Investments (Amortized Cost And Fair Value Of Available-For-Sale and Held-To-Maturity Investment Portfolios) (Detail) - USD ($) $ in Millions | Sep. 30, 2020 | Dec. 31, 2019
--- | --- | ---
Variable Interest Entity Primary Beneficiary [Member] |  |  |
Held To Maturity Securities [Abstract] |  |  |
Total held-to-maturity, amortized cost |  | $ 575 | $ 890
Allowance for Credit Losess |  | 0 |
Gross unrealized gains |  | 0 | 2
Gross unrealized losses |  | 0 | 0
Total held-to-maturity investments, fair value |  | 575 | 892
Other-Than-Temporary Impairments | [1] |  | 0
Corporate Obligations [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |
Held To Maturity Securities [Abstract] |  |  |
Total held-to-maturity, amortized cost |  | 575 | 890
Allowance for Credit Losess |  | 0 |
Gross unrealized gains |  | 0 | 2
Gross unrealized losses |  | 0 | 0
Total held-to-maturity investments, fair value |  | 575 | 892
Other-Than-Temporary Impairments | [1] |  | 0
Fixed Maturities [Member] |  |  |
Available For Sale Securities [Abstract] |  |  |
Total available-for-sale, amortized cost |  | 2,511 | 2,984
Allowance for Credit Losess |  | 0 |
Gross unrealized gains |  | 198 | 126
Gross unrealized losses |  | (8) | (11)
Total available-for-sale, fair value |  | 2,701 | 3,099
Other-than-temporary impairments | [1] |  | 0
Fixed Maturities [Member] | U S Treasury And Government [Member] |  |  |
Available For Sale Securities [Abstract] |  |  |
Total available-for-sale, amortized cost |  | 918 | 838
Allowance for Credit Losess |  | 0 |
Gross unrealized gains |  | 85 | 46
Gross unrealized losses |  | 0 | (2)
Total available-for-sale, fair value |  | 1,003 | 882
Other-than-temporary impairments | [1] |  | 0
Fixed Maturities [Member] | US States And Political Subdivisions [Member] |  |  |
Available For Sale Securities [Abstract] |  |  |
Total available-for-sale, amortized cost |  | 159 | 178
Allowance for Credit Losess |  | 0 |
Gross unrealized gains |  | 31 | 22
Gross unrealized losses |  | 0 | 0
Total available-for-sale, fair value |  | 190 | 200
Other-than-temporary impairments | [1] |  | 0
Fixed Maturities [Member] | Foreign Governments [Member] |  |  |
Available For Sale Securities [Abstract] |  |  |
Total available-for-sale, amortized cost |  | 12 | 8
Allowance for Credit Losess |  | 0 |
Gross unrealized gains |  | 1 | 1
Gross unrealized losses |  | 0 | 0
Total available-for-sale, fair value |  | 13 | 9
Other-than-temporary impairments | [1] |  | 0
Fixed Maturities [Member] | Corporate Obligations [Member] |  |  |
Available For Sale Securities [Abstract] |  |  |
Total available-for-sale, amortized cost |  | 870 | 1,140
Allowance for Credit Losess |  | 0 |
Gross unrealized gains |  | 68 | 52
Gross unrealized losses |  | (4) | (1)
Total available-for-sale, fair value |  | 934 | 1,191
Other-than-temporary impairments | [1] |  | 0
Fixed Maturities [Member] | Residential Mortgage-Backed Agency [Member] |  |  |
Available For Sale Securities [Abstract] |  |  |
Total available-for-sale, amortized cost |  | 281 | 317
Allowance for Credit Losess |  | 0 |
Gross unrealized gains |  | 8 | 3
Gross unrealized losses |  | 0 | 0
Total available-for-sale, fair value |  | 289 | 320
Other-than-temporary impairments | [1] |  | 0
Fixed Maturities [Member] | Residential Mortgage-Backed Non-Agency [Member] |  |  |
Available For Sale Securities [Abstract] |  |  |
Total available-for-sale, amortized cost |  | 23 | 23
Allowance for Credit Losess |  | 0 |
Gross unrealized gains |  | 3 | 1
Gross unrealized losses |  | 0 | (5)
Total available-for-sale, fair value |  | 26 | 19
Other-than-temporary impairments | [1] |  | 0
Fixed Maturities [Member] | Commercial Mortgage-Backed [Member] |  |  |
Available For Sale Securities [Abstract] |  |  |
Total available-for-sale, amortized cost |  | 17 | 20
Allowance for Credit Losess |  | 0 |
Gross unrealized gains |  | 1 | 0
Gross unrealized losses |  | 0 | 0
Total available-for-sale, fair value |  | 18 | 20
Other-than-temporary impairments | [1] |  | 0
Fixed Maturities [Member] | Collateralized Debt Obligations [Member] |  |  |
Available For Sale Securities [Abstract] |  |  |
Total available-for-sale, amortized cost |  | 125 | 139
Allowance for Credit Losess |  | 0 |
Gross unrealized gains |  | 0 | 0
Gross unrealized losses |  | (4) | (2)
Total available-for-sale, fair value |  | 121 | 137
Other-than-temporary impairments | [1] |  | 0
Fixed Maturities [Member] | Other Asset-Backed [Member] |  |  |
Available For Sale Securities [Abstract] |  |  |
Total available-for-sale, amortized cost |  | 106 | 321
Allowance for Credit Losess |  | 0 |
Gross unrealized gains |  | 1 | 1
Gross unrealized losses |  | 0 | (1)
Total available-for-sale, fair value |  | $ 107 | 321
Other-than-temporary impairments | [1] |  | $ 0
[1] | Represents unrealized gains or losses on OTTI 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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