Fair Value Measurement (Details 4) (USD $)	9 Months Ended
	Sep. 30, 2012
Asset-backed securities | Whole business securitization
Quantitative Information About Level 3 Fair Value Measurements
Fair value of assets as of the balance sheet date	$ 54,000,000
Asset-backed securities | Whole business securitization | Discounted cash flow | Minimum
Quantitative Information About Level 3 Fair Value Measurements
Annual gross revenue projections	54,000,000
Liquidity discount (as a percent)	5.00%
Asset-backed securities | Whole business securitization | Discounted cash flow | Maximum
Quantitative Information About Level 3 Fair Value Measurements
Annual gross revenue projections	96,000,000
Liquidity discount (as a percent)	20.00%
Asset-backed securities | Whole business securitization | Discounted cash flow | Weighted Average
Quantitative Information About Level 3 Fair Value Measurements
Value of primary financial guaranty policy (as a percent)	43.80%
Asset-backed securities | Investor-owned utility
Quantitative Information About Level 3 Fair Value Measurements
Fair value of assets as of the balance sheet date	192,000,000
Asset-backed securities | Investor-owned utility | Discounted cash flow | Minimum
Quantitative Information About Level 3 Fair Value Measurements
Liquidation value	174,000,000
Asset-backed securities | Investor-owned utility | Discounted cash flow | Maximum
Quantitative Information About Level 3 Fair Value Measurements
Liquidation value	281,000,000
Years to liquidation	2 years
Asset-backed securities | Investor-owned utility | Discounted cash flow | Weighted Average
Quantitative Information About Level 3 Fair Value Measurements
Discount factor (as a percent)	14.50%
Asset-backed securities | XXX life insurance transactions
Quantitative Information About Level 3 Fair Value Measurements
Fair value of assets as of the balance sheet date	53,000,000
Asset-backed securities | XXX life insurance transactions | Discounted cash flow | Weighted Average
Quantitative Information About Level 3 Fair Value Measurements
Yield (as a percent)	12.80%
Fixed maturity securities | RMBS
Quantitative Information About Level 3 Fair Value Measurements
Fair value of assets as of the balance sheet date	209,000,000
Fixed maturity securities | RMBS | Discounted cash flow | Minimum
Quantitative Information About Level 3 Fair Value Measurements
Loss severity rate (as a percent)	48.00%
CPR (as a percent)	0.80%
CDR (as a percent)	4.40%
Yield (as a percent)	4.30%
Fixed maturity securities | RMBS | Discounted cash flow | Maximum
Quantitative Information About Level 3 Fair Value Measurements
Loss severity rate (as a percent)	102.80%
CPR (as a percent)	7.50%
CDR (as a percent)	28.60%
Yield (as a percent)	14.80%
Fixed maturity securities | Obligations of state and political subdivisions
Quantitative Information About Level 3 Fair Value Measurements
Fair value of assets as of the balance sheet date	11,000,000
Fixed maturity securities | Obligations of state and political subdivisions | Discounted cash flow | Minimum
Quantitative Information About Level 3 Fair Value Measurements
Rate of inflation	1.00%
Assumed sale proceeds (as a percent)	4.90%
Collateral recovery period (in years)	1 month
Fixed maturity securities | Obligations of state and political subdivisions | Discounted cash flow | Maximum
Quantitative Information About Level 3 Fair Value Measurements
Rate of inflation	3.00%
Assumed sale proceeds (as a percent)	29.10%
Collateral recovery period (in years)	10 years
Other invested assets
Quantitative Information About Level 3 Fair Value Measurements
Fair value of assets as of the balance sheet date	8,000,000
Other invested assets | Discounted cash flow | Minimum
Quantitative Information About Level 3 Fair Value Measurements
Prepayment speeds	6.00%
Liquidity discount (as a percent)	10.00%
Recovery on delinquent loans (as a percent)	20.00%
Default rates (as a percent)	1.00%
Loss severity rate (as a percent)	40.00%
Other invested assets | Discounted cash flow | Maximum
Quantitative Information About Level 3 Fair Value Measurements
Prepayment speeds	15.00%
Liquidity discount (as a percent)	20.00%
Recovery on delinquent loans (as a percent)	60.00%
Default rates (as a percent)	10.00%
Loss severity rate (as a percent)	90.00%
Other assets
Quantitative Information About Level 3 Fair Value Measurements
Fair value of assets as of the balance sheet date	42,000,000
Other assets | Discounted cash flow | Minimum
Quantitative Information About Level 3 Fair Value Measurements
Quotes from third party pricing	39
Other assets | Discounted cash flow | Maximum
Quantitative Information About Level 3 Fair Value Measurements
Quotes from third party pricing	44
Other assets | Discounted cash flow | Weighted Average
Quantitative Information About Level 3 Fair Value Measurements
Term	3 years
Financial guaranty variable interest entities | Liabilities
Quantitative Information About Level 3 Fair Value Measurements
Fair value of liabilities as of the balance sheet date	(3,187,000,000)
Financial guaranty variable interest entities | Liabilities | Discounted cash flow | Minimum
Quantitative Information About Level 3 Fair Value Measurements
Loss severity rate (as a percent)	37.50%
CPR (as a percent)	0.00%
CDR (as a percent)	2.60%
Yield (as a percent)	4.60%
Financial guaranty variable interest entities | Liabilities | Discounted cash flow | Maximum
Quantitative Information About Level 3 Fair Value Measurements
Loss severity rate (as a percent)	103.80%
CPR (as a percent)	11.80%
CDR (as a percent)	37.60%
Yield (as a percent)	20.00%
Financial guaranty variable interest entities | Assets
Quantitative Information About Level 3 Fair Value Measurements
Fair value of assets as of the balance sheet date	2,693,000,000
Financial guaranty variable interest entities | Assets | Discounted cash flow | Minimum
Quantitative Information About Level 3 Fair Value Measurements
Loss severity rate (as a percent)	37.50%
CPR (as a percent)	0.00%
CDR (as a percent)	2.60%
Yield (as a percent)	4.60%
Financial guaranty variable interest entities | Assets | Discounted cash flow | Maximum
Quantitative Information About Level 3 Fair Value Measurements
Loss severity rate (as a percent)	103.80%
CPR (as a percent)	11.80%
CDR (as a percent)	37.60%
Yield (as a percent)	20.00%
Credit derivatives | Derivative liabilities, net
Quantitative Information About Level 3 Fair Value Measurements
Fair value of liabilities as of the balance sheet date	$ (1,701,000,000)
Credit derivatives | Derivative liabilities, net | Discounted cash flow | Minimum
Quantitative Information About Level 3 Fair Value Measurements
Year 1 loss estimates (as a percent)	0.00%
Hedge cost (in bps)	1.04%
Bank profit (in bps)	0.01%
Internal floor (in bps)	0.07%
Credit derivatives | Derivative liabilities, net | Discounted cash flow | Maximum
Quantitative Information About Level 3 Fair Value Measurements
Year 1 loss estimates (as a percent)	60.00%
Hedge cost (in bps)	9.04%
Bank profit (in bps)	12.87%
Internal floor (in bps)	0.40%