Fair Value of Assets and Liabilities (Details 2) - Derivatives embedded in life and annuity contracts - Equity-indexed and forward starting options - Stochastic cash flow model - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Quantitative information about the significant unobservable inputs
Liabilities, fair value	$ (253)	$ (247)
Weighted average projected option cost (as a percent)	1.74%	1.75%
Minimum
Quantitative information about the significant unobservable inputs
Projected option cost (as a percent)	1.00%	1.00%
Maximum
Quantitative information about the significant unobservable inputs
Projected option cost (as a percent)	2.20%	2.20%