Fair Value of Assets and Liabilities - Significant unobservable inputs (Details) $ in Millions	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Quantitative information about the significant unobservable inputs
Fair value	$ 21,725	$ 21,400
Significant unobservable inputs (Level 3)
Quantitative information about the significant unobservable inputs
Fair value	208	191
Assets at fair value	324	321
Derivatives embedded in life and annuity contracts – Equity-indexed and forward starting options | Significant unobservable inputs (Level 3)
Quantitative information about the significant unobservable inputs
Derivatives embedded in life and annuity contracts – Equity-indexed and forward starting options	(395)	(184)
Fixed Income Securities Valued Based on Nonbinding Broker Quotes [Member] | Significant unobservable inputs (Level 3)
Quantitative information about the significant unobservable inputs
Assets at fair value	$ 38	$ 80
Projected option cost | Derivatives embedded in life and annuity contracts – Equity-indexed and forward starting options | Significant unobservable inputs (Level 3) | Maximum
Quantitative information about the significant unobservable inputs
Range	0.042	0.022
Projected option cost | Derivatives embedded in life and annuity contracts – Equity-indexed and forward starting options | Significant unobservable inputs (Level 3) | Minimum
Quantitative information about the significant unobservable inputs
Range	0.010	0.010
Projected option cost | Derivatives embedded in life and annuity contracts – Equity-indexed and forward starting options | Significant unobservable inputs (Level 3) | Weighted average
Quantitative information about the significant unobservable inputs
Range	0.0257	0.0174