- Quantitative Information - Assets (Details) (Income Approach Valuation Technique [Member], Level 3 [Member], USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
Obligations of state and political subdivisions [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset, fair value	38	[1]	36	[1]
Obligations of state and political subdivisions [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Rate of inflation (as a percent)	1.00%		1.00%
Cash flow receipts (as a percent)	0.50%		0.50%
Discount factor (as a percent)			4.60%
Yield (as a percent)	4.60%
Collateral recovery period (in years)	1 month		1 month
Obligations of state and political subdivisions [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Rate of inflation (as a percent)	3.00%		3.00%
Cash flow receipts (as a percent)	74.30%		60.90%
Discount factor (as a percent)			9.00%
Yield (as a percent)	8.00%
Collateral recovery period (in years)	34 years		10 years
Obligations of state and political subdivisions [Member] | Weighted Average [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Rate of inflation (as a percent)	2.00%		2.00%
Cash flow receipts (as a percent)	63.00%		51.10%
Discount factor (as a percent)			8.00%
Yield (as a percent)	7.30%
Collateral recovery period (in years)	28 years		3 years
Corporate securities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset, fair value	79	[1]	136	[1]
Yield (as a percent)	17.80%		8.30%
RMBS [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset, fair value	425	[1]	290	[1]
RMBS [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Yield (as a percent)	4.70%		2.50%
Conditional prepayment rate (as a percent)	0.30%		0.98%
Conditional default rate (as a percent)	2.70%		5.00%
Loss severity rate (as a percent)	52.60%		48.10%
RMBS [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Yield (as a percent)	11.70%		9.40%
Conditional prepayment rate (as a percent)	8.10%		15.80%
Conditional default rate (as a percent)	10.60%		25.80%
Loss severity rate (as a percent)	100.00%		102.50%
RMBS [Member] | Weighted Average [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Yield (as a percent)	6.40%		5.70%
Conditional prepayment rate (as a percent)	3.30%		4.10%
Conditional default rate (as a percent)	5.30%		17.90%
Loss severity rate (as a percent)	75.20%		87.20%
Investor-owned utilities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset, fair value	95	[1]	141	[1]
Cash flow receipts (as a percent)			100.00%
Discount factor (as a percent)	7.00%		15.30%
Collateral recovery period (in years)	4 years
Investor-owned utilities [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Collateral recovery period (in years)			12 months
Liquidation value			195
Years to liquidation			0 years
Investor-owned utilities [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Collateral recovery period (in years)			6 years
Liquidation value			245
Years to liquidation			3 years
Investor-owned utilities [Member] | Weighted Average [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Collateral recovery period (in years)			3 years 6 months
Liquidation value			228
Years to liquidation			2 years
XXX life insurance transactions [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset, fair value	133	[1]	127	[1]
Yield (as a percent)	7.30%		12.50%
Other invested assets [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset, fair value	83	[1]	8	[1]
Liquidity discount (as a percent)	20.00%
Recovery on delinquent loans (as a percent)	40.00%
Other invested assets [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Conditional prepayment rate (as a percent)	5.00%		6.00%
Conditional default rate (as a percent)	0.00%		1.00%
Loss severity rate (as a percent)	40.00%		40.00%
Liquidity discount (as a percent)			10.00%
Recovery on delinquent loans (as a percent)			20.00%
Net asset value (per share)	965
Other invested assets [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Conditional prepayment rate (as a percent)	15.00%		15.00%
Conditional default rate (as a percent)	7.00%		10.00%
Loss severity rate (as a percent)	75.00%		90.00%
Liquidity discount (as a percent)			20.00%
Recovery on delinquent loans (as a percent)			60.00%
Net asset value (per share)	1,159
Other invested assets [Member] | Weighted Average [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Conditional prepayment rate (as a percent)	12.30%		13.10%
Conditional default rate (as a percent)	5.80%		3.20%
Loss severity rate (as a percent)	68.30%		73.50%
Liquidity discount (as a percent)			20.00%
Recovery on delinquent loans (as a percent)			40.00%
Net asset value (per share)	1,082
Financial Guaranty Variable Interest Entities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset, fair value	1,398	[1]	2,565	[1]
Financial Guaranty Variable Interest Entities [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Yield (as a percent)	2.70%		3.50%
Conditional prepayment rate (as a percent)	0.30%		0.30%
Conditional default rate (as a percent)	1.60%		3.00%
Loss severity rate (as a percent)	40.00%		37.50%
Financial Guaranty Variable Interest Entities [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Yield (as a percent)	17.70%		10.20%
Conditional prepayment rate (as a percent)	11.00%		11.80%
Conditional default rate (as a percent)	11.80%		25.80%
Loss severity rate (as a percent)	100.00%		102.00%
Financial Guaranty Variable Interest Entities [Member] | Weighted Average [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Yield (as a percent)	7.90%		5.40%
Conditional prepayment rate (as a percent)	3.30%		3.60%
Conditional default rate (as a percent)	5.10%		13.60%
Loss severity rate (as a percent)	82.20%		94.60%
Other Assets [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset, fair value	35	[1]	46	[1]
Fair Value Inputs Term	5 years		5 years
Other Assets [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Quotes from third party pricing (in dollars per share)	52		47
Other Assets [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Quotes from third party pricing (in dollars per share)	61		53
Other Assets [Member] | Weighted Average [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Quotes from third party pricing (in dollars per share)	57		50

[1] (1)Discounted cash flow is used as valuation technique for all financial instruments.