- Quantitative Information - Liabilities (Details) - Income Approach Valuation Technique [Member] - USD ($) $ in Millions		9 Months Ended	12 Months Ended
		Sep. 30, 2015	Dec. 31, 2014
Credit derivative liabilities, net [Member] | Level 3 [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Total liabilities carried at fair value	[1]	$ (847)	$ (895)
Credit derivative liabilities, net [Member] | Minimum [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Internal floor (as a percent)		0.07%	0.07%
Bank profit (as a percent)		0.038%	0.01%
Hedge cost (as a percent)		0.26%	0.20%
Credit derivative liabilities, net [Member] | Minimum [Member] | Level 3 [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Year 1 loss estimates (as a percent)		0.00%	0.00%
Credit derivative liabilities, net [Member] | Maximum [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Internal floor (as a percent)		1.00%	1.00%
Bank profit (as a percent)		11.704%	9.944%
Hedge cost (as a percent)		2.528%	2.438%
Credit derivative liabilities, net [Member] | Maximum [Member] | Level 3 [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Year 1 loss estimates (as a percent)		100.00%	93.00%
Credit derivative liabilities, net [Member] | Weighted Average [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Internal floor (as a percent)		0.256%	0.159%
Bank profit (as a percent)		1.489%	1.27%
Hedge cost (as a percent)		0.64%	0.615%
Credit derivative liabilities, net [Member] | Weighted Average [Member] | Level 3 [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Year 1 loss estimates (as a percent)		4.00%	2.10%
Financial Guaranty Variable Interest Entities [Member] | Level 3 [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Total liabilities carried at fair value	[1]	$ (1,482)	$ (1,419)
Financial Guaranty Variable Interest Entities [Member] | Minimum [Member] | Level 3 [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Loss severity rate (as a percent)		40.00%	40.00%
Conditional default rate (as a percent)		1.00%	1.60%
Conditional prepayment rate (as a percent)		0.30%	0.30%
Yield (as a percent)		1.50%	2.70%
Financial Guaranty Variable Interest Entities [Member] | Maximum [Member] | Level 3 [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Loss severity rate (as a percent)		100.00%	100.00%
Conditional default rate (as a percent)		22.00%	11.80%
Conditional prepayment rate (as a percent)		12.00%	11.00%
Yield (as a percent)		17.30%	17.70%
Financial Guaranty Variable Interest Entities [Member] | Weighted Average [Member] | Level 3 [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Loss severity rate (as a percent)		81.70%	82.20%
Conditional default rate (as a percent)		4.80%	5.10%
Conditional prepayment rate (as a percent)		3.60%	3.30%
Yield (as a percent)		5.40%	5.80%

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