Fair Value (Quantitative information about significant unobservable inputs in the fair value measurement of level 3 assets) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012
Equity securities [Member]
Fair Value Inputs, Quantitative Information
Fair value	$ 69
Valuation technique(s)	Market approach
Unobservable input(s)	Private offering price
Range (weighted average)	$0.10 - $4,023 per share ($211.01 per share)
Life settlement contracts [Member]
Fair Value Inputs, Quantitative Information
Fair value	115
Valuation technique(s)	Discounted cash flow
Unobservable input(s)	Discount rate risk premium Mortality assumption
Range (weighted average)	9% 65% - 928% (181%)
Discounted cash flow valuation [Member] | Fixed maturity securities [Member]
Fair Value Inputs, Quantitative Information
Fair value	204
Valuation technique(s)	Discounted cash flow
Unobservable Input(s)	Expected call date assumption
Range (weighted average)	0.5 - 5.5 years (2.2 years)
Market approach valuation [Member] | Fixed maturity securities [Member]
Fair Value Inputs, Quantitative Information
Fair value	$ 53
Valuation technique(s)	Market approach
Unobservable input(s)	Private offering price
Range (weighted average)	$26.5 million per unit