Investments (Details 8) (USD $) In Millions, unless otherwise specified	Sep. 30, 2011	Dec. 31, 2010
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
% of Total	100.00%	100.00%
Fixed rate mortgage loans collateral [Member] | Alternative residential mortgage loans [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
% of Total	92.70%	90.70%
Hybrid adjustable rate mortgage loans collateral [Member] | Alternative residential mortgage loans [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
% of Total	7.30%	9.30%
Alternative residential mortgage loans [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Net unrealized gains (losses)	$ (824)	$ (670)
% of Total	100.00%	100.00%
Alternative residential mortgage loans [Member] | Rated Aa/AA or Better [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
% of Total	12.70%	15.90%
Alternative residential mortgage loans [Member] | NAIC 1 [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
% of Total	47.10%	39.50%