Fair Value of Assets and Liabilities - Quantitative information about Level 3 instruments (Details) - Equity-indexed and forward starting options in life and annuity product contracts - Significant unobservable inputs (Level 3) $ in Millions	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Quantitative information about the significant unobservable inputs
Fair value	$ (483)	$ (430)
Projected option cost | Minimum
Quantitative information about the significant unobservable inputs
Weighted average	0.010	0.010
Projected option cost | Maximum
Quantitative information about the significant unobservable inputs
Weighted average	0.042	0.042
Projected option cost | Weighted Average
Quantitative information about the significant unobservable inputs
Weighted average	0.0280	0.0267