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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, 2020 | Dec. 31, 2019
--- | --- | ---
Variable Interest Entity Primary Beneficiary [Member] |  |  |
Held To Maturity Securities [Abstract] |  |  |
Total held-to-maturity, amortized cost |  |  | $ 890
Gross unrealized gains |  |  | 2
Gross unrealized losses |  |  | 0
Total held-to-maturity investments, fair value |  | $ 0 | 892
Other-Than-Temporary Impairments |  |  | 0
Corporate Obligations [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |
Held To Maturity Securities [Abstract] |  |  |
Total held-to-maturity, amortized cost |  |  | 890
Gross unrealized gains |  |  | 2
Gross unrealized losses |  |  | 0
Total held-to-maturity investments, fair value |  |  | 892
Other-Than-Temporary Impairments |  |  | 0
Fixed Maturities [Member] |  |  |
Available For Sale Securities [Abstract] |  |  |
Total available-for-sale, amortized cost |  | 2,360 | 2,984
Allowance for Credit Losess |  | 0 |
Gross unrealized gains |  | 184 | 126
Gross unrealized losses |  | (5) | (11)
Total available-for-sale, fair value |  | 2,539 | 3,099
Other-than-temporary impairments |  |  | 0
Fixed Maturities [Member] | U S Treasury And Government [Member] |  |  |
Available For Sale Securities [Abstract] |  |  |
Total available-for-sale, amortized cost |  | 775 | 838
Allowance for Credit Losess |  | 0 |
Gross unrealized gains |  | 75 | 46
Gross unrealized losses |  | (1) | (2)
Total available-for-sale, fair value |  | 849 | 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 |  | 162 | 178
Allowance for Credit Losess |  | 0 |
Gross unrealized gains |  | 32 | 22
Gross unrealized losses |  | 0 | 0
Total available-for-sale, fair value |  | 194 | 200
Other-than-temporary impairments | [1] |  | 0
Fixed Maturities [Member] | Foreign Governments [Member] |  |  |
Available For Sale Securities [Abstract] |  |  |
Total available-for-sale, amortized cost |  | 11 | 8
Allowance for Credit Losess |  | 0 |
Gross unrealized gains |  | 1 | 1
Gross unrealized losses |  | 0 | 0
Total available-for-sale, fair value |  | 12 | 9
Other-than-temporary impairments | [1] |  | 0
Fixed Maturities [Member] | Corporate Obligations [Member] |  |  |
Available For Sale Securities [Abstract] |  |  |
Total available-for-sale, amortized cost |  | 827 | 1,140
Allowance for Credit Losess |  | 0 |
Gross unrealized gains |  | 64 | 52
Gross unrealized losses |  | (1) | (1)
Total available-for-sale, fair value |  | 890 | 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 |  | 305 | 317
Allowance for Credit Losess |  | 0 |
Gross unrealized gains |  | 8 | 3
Gross unrealized losses |  | (1) | 0
Total available-for-sale, fair value |  | 312 | 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 |  | 22 | 23
Allowance for Credit Losess |  | 0 |
Gross unrealized gains |  | 3 | 1
Gross unrealized losses |  | 0 | (5)
Total available-for-sale, fair value |  | 25 | 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 |  |  | 0
Fixed Maturities [Member] | Collateralized Debt Obligations [Member] |  |  |
Available For Sale Securities [Abstract] |  |  |
Total available-for-sale, amortized cost |  | 120 | 139
Allowance for Credit Losess |  | 0 |
Gross unrealized gains |  | 0 | 0
Gross unrealized losses |  | (2) | (2)
Total available-for-sale, fair value |  | 118 | 137
Other-than-temporary impairments |  |  | 0
Fixed Maturities [Member] | Other Asset-Backed [Member] |  |  |
Available For Sale Securities [Abstract] |  |  |
Total available-for-sale, amortized cost |  | 121 | 321
Allowance for Credit Losess |  | 0 |
Gross unrealized gains |  | 0 | 1
Gross unrealized losses |  | 0 | (1)
Total available-for-sale, fair value |  | $ 121 | 321
Other-than-temporary impairments |  |  | $ 0
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