- Quantitative Information - Assets (Details) - Income Approach Valuation Technique [Member] - Level 3 [Member] - USD ($) $ / shares in Units, $ in Millions		9 Months Ended		12 Months Ended
		Sep. 30, 2015		Dec. 31, 2014
Obligations of state and political subdivisions [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset, fair value	[1]	$ 8		$ 38
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%
Cash flow receipts (as a percent)				0.50%
Yield (as a percent)				4.60%
Collateral recovery period (in years)				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%
Cash flow receipts (as a percent)				74.30%
Yield (as a percent)				8.00%
Collateral recovery period (in years)				34 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%
Cash flow receipts (as a percent)				63.00%
Yield (as a percent)				7.30%
Collateral recovery period (in years)				28 years
Corporate securities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset, fair value	[1]	$ 79	[2]	$ 79
Yield (as a percent)		20.60%	[2]	17.80%
RMBS [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset, fair value	[1]	$ 361	[2]	$ 425
RMBS [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Yield (as a percent)		4.30%	[2]	4.70%
Conditional prepayment rate (as a percent)		0.30%	[2]	0.30%
Conditional default rate (as a percent)		2.60%	[2]	2.70%
Loss severity rate (as a percent)		60.00%	[2]	52.60%
RMBS [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Yield (as a percent)		7.80%	[2]	11.70%
Conditional prepayment rate (as a percent)		8.20%	[2]	8.10%
Conditional default rate (as a percent)		11.90%	[2]	10.60%
Loss severity rate (as a percent)		100.00%	[2]	100.00%
RMBS [Member] | Weighted Average [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Yield (as a percent)		5.70%	[2]	6.40%
Conditional prepayment rate (as a percent)		2.60%	[2]	3.30%
Conditional default rate (as a percent)		5.90%	[2]	5.30%
Loss severity rate (as a percent)		75.60%	[2]	75.20%
Investor-owned utilities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset, fair value	[1]	$ 99	[2]	$ 95
Cash flow receipts (as a percent)		100.00%	[2]	100.00%
Discount factor (as a percent)		7.00%	[2]	7.00%
Collateral recovery period (in years)		3 years 3 months	[2]	4 years
Triple-X Life Insurance Transaction [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset, fair value	[1]	$ 336	[2]	$ 133
XXX life insurance transactions [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Yield (as a percent)				7.30%
XXX life insurance transactions [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Yield (as a percent)	[2]	3.00%
XXX life insurance transactions [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Yield (as a percent)	[2]	7.00%
XXX life insurance transactions [Member] | Weighted Average [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Yield (as a percent)	[2]	4.50%
Short-term Investments [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset, fair value	[1]	$ 50
Yield (as a percent)		15.00%
Alternative Other Invested Asset [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset, fair value	[1],[3]	$ 45
Alternative Other Invested Asset [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Net asset value (per share)	[3]	$ 906
Alternative Other Invested Asset [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Net asset value (per share)	[3]	1,113
Alternative Other Invested Asset [Member] | Weighted Average [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Net asset value (per share)	[3]	$ 998
Other invested assets [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset, fair value		$ 8	[4]	$ 83	[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%
Conditional default rate (as a percent)				0.00%
Loss severity rate (as a percent)				40.00%
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%
Conditional default rate (as a percent)				7.00%
Loss severity rate (as a percent)				75.00%
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%
Conditional default rate (as a percent)				5.80%
Loss severity rate (as a percent)				68.30%
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]	$ 1,541		$ 1,398
Financial Guaranty Variable Interest Entities [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Yield (as a percent)		1.50%		2.70%
Conditional prepayment rate (as a percent)		0.30%		0.30%
Conditional default rate (as a percent)		1.00%		1.60%
Loss severity rate (as a percent)		40.00%		40.00%
Financial Guaranty Variable Interest Entities [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Yield (as a percent)		17.30%		17.70%
Conditional prepayment rate (as a percent)		12.00%		11.00%
Conditional default rate (as a percent)		22.00%		11.80%
Loss severity rate (as a percent)		100.00%		100.00%
Financial Guaranty Variable Interest Entities [Member] | Weighted Average [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Yield (as a percent)		6.30%		7.90%
Conditional prepayment rate (as a percent)		3.60%		3.30%
Conditional default rate (as a percent)		4.80%		5.10%
Loss severity rate (as a percent)		81.70%		82.20%
Other Assets [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Asset, fair value	[1]	$ 45		$ 35
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)		$ 48		$ 52
Other Assets [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Quotes from third party pricing (in dollars per share)		53		61
Other Assets [Member] | Weighted Average [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Quotes from third party pricing (in dollars per share)		$ 51		$ 57

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

[2] Excludes obligations of state and political subdivisions investments with fair value of $8 million.

[3] Excludes several investments with fair value of $8 million.

[4] Discounted cash flow is used as valuation technique for all financial instruments.