Fair Value (Quantitative information about significant unobservable inputs in the fair value measurement of level 3 assets) (Details) (USD $)	Mar. 31, 2013	Dec. 31, 2012
Fixed maturity securities [Member] | Discounted cash flow valuation technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	$ 78,000,000	$ 121,000,000
Fixed maturity securities [Member] | Discounted cash flow valuation technique [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected call date	3.0	3.3
Credit spread adjustment	0.02%	0.02%
Fixed maturity securities [Member] | Discounted cash flow valuation technique [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected call date	4.6	5.3
Credit spread adjustment	0.48%	0.48%
Fixed maturity securities [Member] | Discounted cash flow valuation technique [Member] | Weighted Average [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected call date	4.0	4.3
Credit spread adjustment	0.17%	0.17%
Fixed maturity securities [Member] | Market approach valuation technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	97,000,000	72,000,000
Fixed maturity securities [Member] | Market approach valuation technique [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Private offering price	$ 34.70	$ 42.39
Fixed maturity securities [Member] | Market approach valuation technique [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Private offering price	$ 122.09	$ 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	$ 102.97	$ 100.11
Equity securities [Member] | Market approach valuation technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	19,000,000	34,000,000
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	$ 3,970.99	$ 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	$ 1,114.32	$ 571.17
Life settlement contracts [Member] | Discounted cash flow valuation technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	$ 95,000,000	$ 100,000,000
Life settlement contracts [Member] | Discounted cash flow valuation technique [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Mortality assumption	69.00%	69.00%
Life settlement contracts [Member] | Discounted cash flow valuation technique [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Mortality assumption	883.00%	883.00%
Life settlement contracts [Member] | Discounted cash flow valuation technique [Member] | Weighted Average [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Mortality assumption	209.20%	208.90%
Life settlement contracts [Member] | Discounted cash flow valuation technique [Member] | Rate [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate risk premium	9.00%	9.00%