Fair Value of Assets and Liabilities - Significant unobservable inputs (Details) $ in Millions	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Quantitative information about the significant unobservable inputs
Fair value	$ 21,400	$ 23,261
Significant unobservable inputs (Level 3)
Quantitative information about the significant unobservable inputs
Fair value	191	376
Assets at fair value	321	467
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	(184)	(250)
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	$ 80	$ 237
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	0.022	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	0.0174	0.0174