Investments (Held-to-maturity credit quality indicator) (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
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%