Fair Value of Assets and Liabilities (Level 3 Fair Value Measurment) (Details) - Significant unobservable inputs (Level 3) - Derivatives embedded in life and annuity contracts - Equity-indexed and forward starting options - Stochastic cash flow model - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Quantitative information about the significant unobservable inputs
Fair value	$ (245)	$ (247)
Weighted average projected option cost (as a percent)	1.75%	1.76%
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%