Fair Value (Quantitative information about significant unobservable inputs in the fair value measurement of level 3 assets) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Fixed maturity securities [Member] | Income Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	$ 106	$ 121
Fixed maturity securities [Member] | Income Approach Valuation Technique [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected call date	1.6	3.3
Credit spread adjustment		0.02%
Credit spread	1.95%
Fixed maturity securities [Member] | Income Approach Valuation Technique [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected call date	3.5	5.3
Credit spread adjustment		0.48%
Credit spread	7.95%
Fixed maturity securities [Member] | Income Approach Valuation Technique [Member] | Weighted Average [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected call date	3.1	4.3
Credit spread adjustment		0.17%
Credit spread	2.67%
Fixed maturity securities [Member] | Market approach valuation technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	83	72
Fixed maturity securities [Member] | Market approach valuation technique [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Private offering price	$ 36.32	$ 42.39
Fixed maturity securities [Member] | Market approach valuation technique [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Private offering price	$ 113.76	$ 102.32
Fixed maturity securities [Member] | Market approach valuation technique [Member] | Weighted Average [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Private offering price	$ 101.70	$ 100.11
Equity securities [Member] | Market approach valuation technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	13	34
Equity securities [Member] | Market approach valuation technique [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Private offering price	$ 33.73	$ 4.54
Equity securities [Member] | Market approach valuation technique [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Private offering price	$ 4,017.00	$ 3,842.00
Equity securities [Member] | Market approach valuation technique [Member] | Weighted Average [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Private offering price	$ 936.89	$ 571.17
Life settlement contracts [Member] | Income Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	$ 91	$ 100
Life settlement contracts [Member] | Income Approach Valuation Technique [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Mortality assumption	69.00%	69.00%
Life settlement contracts [Member] | Income Approach Valuation Technique [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Mortality assumption	883.00%	883.00%
Life settlement contracts [Member] | Income Approach Valuation Technique [Member] | Weighted Average [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Mortality assumption	209.20%	208.90%
Life settlement contracts [Member] | Income Approach Valuation Technique [Member] | Rate [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate risk premium	9.00%	9.00%