Fair Values of Assets and Liabilities (Details 3) (Discounted cash flow, USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
GMWB and GMAB embedded derivatives
Fair values of assets and liabilities
Fair Value	$ 266	$ 833
Nonperformance risk (as a percent)	0.93%	0.97%
GMWB and GMAB embedded derivatives | Minimum
Fair values of assets and liabilities
Utilization of guaranteed withdrawals (as a percent)	0.00%	0.00%
Surrender rate (as a percent)	0.00%	0.00%
Market volatility (as a percent)	5.20%	5.60%
GMWB and GMAB embedded derivatives | Maximum
Fair values of assets and liabilities
Utilization of guaranteed withdrawals (as a percent)	56.40%	56.40%
Surrender rate (as a percent)	56.30%	56.30%
Market volatility (as a percent)	20.20%	21.20%
Corporate debt securities (private placements)
Fair values of assets and liabilities
Fair Value	$ 1,625	$ 1,624
Corporate debt securities (private placements) | Minimum
Fair values of assets and liabilities
Yield/spread to U.S. Treasuries (as a percent)	1.10%	1.10%
Corporate debt securities (private placements) | Maximum
Fair values of assets and liabilities
Yield/spread to U.S. Treasuries (as a percent)	6.00%	8.50%
Corporate debt securities (private placements) | Weighted Average
Fair values of assets and liabilities
Yield/spread to U.S. Treasuries (as a percent)	2.00%	2.20%