Expected Loss to be Paid - Key Assumptions in Base Case Expected Loss (Details) - Residential Mortgage-Backed Securities (RMBS) [Member] - United States [Member] - Home equity lines of credit (HELOCs) [Member]		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Expected Losses to be Paid [Line Items]
Loss severity	[1]	98.00%	98.00%
Minimum [Member]
Schedule of Expected Losses to be Paid [Line Items]
Plateau CDR	[1]	3.50%	4.90%	2.80%
Final CDR trended down to	[1]	0.50%	0.50%	0.50%
Loss severity	[1]			90.00%
Maximum [Member]
Schedule of Expected Losses to be Paid [Line Items]
Plateau CDR	[1]	24.80%	23.50%	6.80%
Final CDR trended down to	[1]	3.20%	3.20%	3.20%
Loss severity	[1]			98.00%
Weighted Average [Member]
Schedule of Expected Losses to be Paid [Line Items]
Plateau CDR	[1]	13.60%	10.30%	4.10%
Final CDR trended down to	[1]	1.30%	1.20%	1.20%
Loss severity	[1]			90.40%
Financing Receivable, Modified in Previous 12 Months [Member]
Schedule of Expected Losses to be Paid [Line Items]
Insured Financial Obligations, Projected Loss Assumptions, Liquidation Rate		25.00%	25.00%	25.00%
Financing Receivable, Delinquent in the Previous 12 Months [Member]
Schedule of Expected Losses to be Paid [Line Items]
Insured Financial Obligations, Projected Loss Assumptions, Liquidation Rate		25.00%	25.00%	25.00%
Financing Receivables, 30 to 59 Days Past Due [Member]
Schedule of Expected Losses to be Paid [Line Items]
Insured Financial Obligations, Projected Loss Assumptions, Liquidation Rate		50.00%	50.00%	55.00%
Financing Receivables, 60 to 89 Days Past Due [Member]
Schedule of Expected Losses to be Paid [Line Items]
Insured Financial Obligations, Projected Loss Assumptions, Liquidation Rate		65.00%	65.00%	70.00%
Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Schedule of Expected Losses to be Paid [Line Items]
Insured Financial Obligations, Projected Loss Assumptions, Liquidation Rate		80.00%	75.00%	80.00%
Financing Receivables, Bankruptcy [Member]
Schedule of Expected Losses to be Paid [Line Items]
Insured Financial Obligations, Projected Loss Assumptions, Liquidation Rate		55.00%	55.00%	55.00%
Financing Receivable, Foreclosure [Member]
Schedule of Expected Losses to be Paid [Line Items]
Insured Financial Obligations, Projected Loss Assumptions, Liquidation Rate		75.00%	75.00%	75.00%
Financing Receivable, Real Estate Owned [Member]
Schedule of Expected Losses to be Paid [Line Items]
Insured Financial Obligations, Projected Loss Assumptions, Liquidation Rate		100.00%	100.00%	100.00%

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