Expected Loss to be Paid - Liquidation Rates and Key Assumptions in Base Case Expected Loss First Lien RMBS (Details)	3 Months Ended		12 Months Ended
	Mar. 31, 2015		Dec. 31, 2014
Financing Receivable, Modified in Previous 12 Months [Member] | Alt-A and Prime [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liquidation Rate	25.00%		25.00%
Financing Receivable, Modified in Previous 12 Months [Member] | Option ARM [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liquidation Rate	25.00%		25.00%
Financing Receivable, Modified in Previous 12 Months [Member] | Subprime [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liquidation Rate	25.00%		25.00%
Financing Receivable, Delinquent in the Previous 12 Months [Member] | Alt-A and Prime [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liquidation Rate	25.00%		25.00%
Financing Receivable, Delinquent in the Previous 12 Months [Member] | Option ARM [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liquidation Rate	25.00%		25.00%
Financing Receivable, Delinquent in the Previous 12 Months [Member] | Subprime [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liquidation Rate	25.00%		25.00%
Financing Receivables, 30 to 59 Days Past Due [Member] | Alt-A and Prime [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liquidation Rate	35.00%		35.00%
Financing Receivables, 30 to 59 Days Past Due [Member] | Option ARM [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liquidation Rate	40.00%		40.00%
Financing Receivables, 30 to 59 Days Past Due [Member] | Subprime [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liquidation Rate	35.00%		35.00%
Financing Receivables, 60 to 89 Days Past Due [Member] | Alt-A and Prime [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liquidation Rate	50.00%		50.00%
Financing Receivables, 60 to 89 Days Past Due [Member] | Option ARM [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liquidation Rate	55.00%		55.00%
Financing Receivables, 60 to 89 Days Past Due [Member] | Subprime [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liquidation Rate	40.00%		40.00%
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Alt-A and Prime [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liquidation Rate	60.00%		60.00%
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Option ARM [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liquidation Rate	65.00%		65.00%
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Subprime [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liquidation Rate	55.00%		55.00%
Financing Receivables, Bankruptcy [Member] | Alt-A and Prime [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liquidation Rate	45.00%		45.00%
Financing Receivables, Bankruptcy [Member] | Option ARM [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liquidation Rate	50.00%		50.00%
Financing Receivables, Bankruptcy [Member] | Subprime [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liquidation Rate	40.00%		40.00%
Financing Receivable, Foreclosure [Member] | Alt-A and Prime [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liquidation Rate	75.00%		75.00%
Financing Receivable, Foreclosure [Member] | Option ARM [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liquidation Rate	80.00%		80.00%
Financing Receivable, Foreclosure [Member] | Subprime [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liquidation Rate	70.00%		70.00%
Financing Receivable, Real Estate Owned [Member]
Schedule of Expected Losses to be Paid [Line Items]
Liquidation Rate	100.00%		100.00%
United States [Member] | Subprime [Member] | RMBS [Member]
Schedule of Expected Losses to be Paid [Line Items]
Period until intermediate CDR	48 months	[1]	48 months	[1]
Final CPR	15.00%	[1],[2]	15.00%	[1],[2]
United States [Member] | Subprime [Member] | 2005 and prior [Member] | RMBS [Member]
Schedule of Expected Losses to be Paid [Line Items]
Initial loss severity	75.00%	[1]	75.00%	[1]
United States [Member] | Subprime [Member] | 2006 [Member] | RMBS [Member]
Schedule of Expected Losses to be Paid [Line Items]
Initial loss severity	90.00%	[1]	90.00%	[1]
United States [Member] | Subprime [Member] | 2007 [Member] | RMBS [Member]
Schedule of Expected Losses to be Paid [Line Items]
Initial loss severity	90.00%	[1]	90.00%	[1]
United States [Member] | Subprime [Member] | Minimum [Member] | RMBS [Member]
Schedule of Expected Losses to be Paid [Line Items]
Plateau CDR	4.80%	[1]	4.90%	[1]
Intermediate CDR	1.00%	[1]	1.00%	[1]
Final CDR	0.20%	[1]	0.20%	[1]
Initial CPR	0.00%	[1]	0.00%	[1]
United States [Member] | Subprime [Member] | Maximum [Member] | RMBS [Member]
Schedule of Expected Losses to be Paid [Line Items]
Plateau CDR	14.40%	[1]	15.00%	[1]
Intermediate CDR	2.90%	[1]	3.00%	[1]
Final CDR	0.70%	[1]	0.70%	[1]
Initial CPR	9.70%	[1]	10.50%	[1]
United States [Member] | Subprime [Member] | Weighted Average [Member] | RMBS [Member]
Schedule of Expected Losses to be Paid [Line Items]
Plateau CDR	10.20%	[1]	10.60%	[1]
Intermediate CDR	2.00%	[1]	2.10%	[1]
Final CDR	0.40%	[1]	0.40%	[1]
Initial CPR	4.70%	[1]	6.10%	[1]
United States [Member] | Option ARM [Member] | RMBS [Member]
Schedule of Expected Losses to be Paid [Line Items]
Period until intermediate CDR	48 months	[1]	48 months	[1]
Final CPR	15.00%	[1],[2]	15.00%	[1],[2]
United States [Member] | Option ARM [Member] | 2005 and prior [Member] | RMBS [Member]
Schedule of Expected Losses to be Paid [Line Items]
Initial loss severity	60.00%	[1]	60.00%	[1]
United States [Member] | Option ARM [Member] | 2006 [Member] | RMBS [Member]
Schedule of Expected Losses to be Paid [Line Items]
Initial loss severity	70.00%	[1]	70.00%	[1]
United States [Member] | Option ARM [Member] | 2007 [Member] | RMBS [Member]
Schedule of Expected Losses to be Paid [Line Items]
Initial loss severity	65.00%	[1]	65.00%	[1]
United States [Member] | Option ARM [Member] | Minimum [Member] | RMBS [Member]
Schedule of Expected Losses to be Paid [Line Items]
Plateau CDR	4.50%	[1]	4.30%	[1]
Intermediate CDR	0.90%	[1]	0.90%	[1]
Final CDR	0.20%	[1]	0.20%	[1]
Initial CPR	1.80%	[1]	1.10%	[1]
United States [Member] | Option ARM [Member] | Maximum [Member] | RMBS [Member]
Schedule of Expected Losses to be Paid [Line Items]
Plateau CDR	12.90%	[1]	14.20%	[1]
Intermediate CDR	2.60%	[1]	2.80%	[1]
Final CDR	0.60%	[1]	0.70%	[1]
Initial CPR	12.70%	[1]	11.80%	[1]
United States [Member] | Option ARM [Member] | Weighted Average [Member] | RMBS [Member]
Schedule of Expected Losses to be Paid [Line Items]
Plateau CDR	9.90%	[1]	10.60%	[1]
Intermediate CDR	2.00%	[1]	2.10%	[1]
Final CDR	0.50%	[1]	0.50%	[1]
Initial CPR	4.90%	[1]	4.90%	[1]
United States [Member] | Alt-A [Member] | RMBS [Member]
Schedule of Expected Losses to be Paid [Line Items]
Period until intermediate CDR	48 months	[1]	48 months	[1]
Final CPR			15.00%	[1],[2]
United States [Member] | Alt-A [Member] | 2005 and prior [Member] | RMBS [Member]
Schedule of Expected Losses to be Paid [Line Items]
Initial loss severity	60.00%	[1]	60.00%	[1]
United States [Member] | Alt-A [Member] | 2006 [Member] | RMBS [Member]
Schedule of Expected Losses to be Paid [Line Items]
Initial loss severity	70.00%	[1]	70.00%	[1]
United States [Member] | Alt-A [Member] | 2007 [Member] | RMBS [Member]
Schedule of Expected Losses to be Paid [Line Items]
Initial loss severity	65.00%	[1]	65.00%	[1]
United States [Member] | Alt-A [Member] | Minimum [Member] | RMBS [Member]
Schedule of Expected Losses to be Paid [Line Items]
Plateau CDR	2.60%	[1]	2.00%	[1]
Intermediate CDR	0.50%	[1]	0.40%	[1]
Final CDR	0.10%	[1]	0.10%	[1]
Initial CPR	2.70%	[1]	1.70%	[1]
Final CPR	15.00%	[1],[2]
United States [Member] | Alt-A [Member] | Maximum [Member] | RMBS [Member]
Schedule of Expected Losses to be Paid [Line Items]
Plateau CDR	13.10%	[1]	13.40%	[1]
Intermediate CDR	2.60%	[1]	2.70%	[1]
Final CDR	0.70%	[1]	0.70%	[1]
Initial CPR	22.40%	[1]	21.00%	[1]
Final CPR	22.40%	[1],[2]
United States [Member] | Alt-A [Member] | Weighted Average [Member] | RMBS [Member]
Schedule of Expected Losses to be Paid [Line Items]
Plateau CDR	7.40%	[1]	7.30%	[1]
Intermediate CDR	1.50%	[1]	1.50%	[1]
Final CDR	0.30%	[1]	0.30%	[1]
Initial CPR	8.10%	[1]	7.70%	[1]
Final CPR	15.20%	[1],[2]

[1] Represents variables for most heavily weighted scenario (the “base case”).

[2] For transactions where the initial CPR is higher than the final CPR, the initial CPR is held constant and the final CPR is not used.