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Investments (Held-to-maturity credit quality indicator) (Detail) - USD ($) $ in Millions | Dec. 31, 2020 | Dec. 31, 2019
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Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items] |  |
Debt Securities, Held-to-maturity | $ 11,697 | $ 12,581
Fixed Maturities Percent of Total Amortized cost | 100.00% |
Standard & Poor's, AAA Rating [Member] |  |
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items] |  |
Debt Securities, Held-to-maturity | $ 2,511 |
Fixed Maturities Percent of Total Amortized cost | 22.00% |
Standard & Poor's, AA Rating [Member] |  |
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items] |  |
Debt Securities, Held-to-maturity | $ 6,193 |
Fixed Maturities Percent of Total Amortized cost | 53.00% |
Standard & Poor's, A Rating [Member] |  |
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items] |  |
Debt Securities, Held-to-maturity | $ 2,138 |
Fixed Maturities Percent of Total Amortized cost | 18.00% |
Standard & Poor's, BBB Rating [Member] |  |
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items] |  |
Debt Securities, Held-to-maturity | $ 826 |
Fixed Maturities Percent of Total Amortized cost | 7.00% |
Standard & Poor's, BB Rating [Member] |  |
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items] |  |
Debt Securities, Held-to-maturity | $ 28 |
Fixed Maturities Percent of Total Amortized cost | 0.00% |
Other [Member] |  |
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items] |  |
Debt Securities, Held-to-maturity | $ 1 |
Fixed Maturities Percent of Total Amortized cost | 0.00% |

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