Expected Losses to be Paid - First Lien Liquidation Rates (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended		9 Months Ended		12 Months Ended
	Jun. 30, 2014		Sep. 30, 2014		Dec. 31, 2013
Projected Loss Assumptions, First Lien Liquidation Rates [Abstract]
All	100.00%		100.00%		100.00%
Projected Loss Assumptions Text One [Abstract]
Expected loan losses, number of payments behind or in foreclosure			2
Period until which loss severity rate would continue (in months)			18 months
Period from initial to final conditional prepayment rate (in months)			2 years 6 months
Alt-A first lien
Projected Loss Assumptions, Base Case Expected Loss Estimates, First Lien RMBS [Abstract]
Period until intermediate CDR	48 months		48 months		48 months
Initial loss severity	65.00%	[1]	65.00%	[1]	65.00%	[1]
Final CPR(2)	15.00%	[1],[2]	15.00%	[1],[2]	15.00%	[1],[2]
Total first lien
Projected Loss Assumptions Text One [Abstract]
Period for constant conditional default rate (in months)			36 months
Period for which estimated defaults are attributed to loans currently delinquent or in foreclosure			36 months
Estimated loss severity rate, one through six months after period end			90.00%
Estimated loss severity rate, six through twelve months after period end			80.00%
Period from initial to final conditional prepayment rate (in months)			12 months
Projected Loss Assumptions Text Two [Abstract]
Current conditional prepayment rate used in alternate scenario for loss estimate (as a percent)			15.00%
Loss severity recovery period used to calculate potential change in loss estimate in even more stressful scenario (in years)			9 years
Decrease in the plateau period used to calculate potential change in loss estimate (in months)			6 months
Decreased plateau period used to calculate potential change in loss estimate (in months)			30 months
Alt- A and Prime
Projected Loss Assumptions, First Lien Liquidation Rates [Abstract]
Current Loans Modified in Previous 12 Months	35.00%		35.00%		35.00%
30 – 59 Days Delinquent	50.00%		50.00%		50.00%
60 – 89 Days Delinquent	60.00%		60.00%		60.00%
90 Days Delinquent	75.00%		75.00%		75.00%
Bankruptcy	60.00%		60.00%		60.00%
Foreclosure	85.00%		85.00%		85.00%
Option ARM
Projected Loss Assumptions, First Lien Liquidation Rates [Abstract]
Current Loans Modified in Previous 12 Months	35.00%		35.00%		35.00%
30 – 59 Days Delinquent	50.00%		50.00%		50.00%
60 – 89 Days Delinquent	65.00%		65.00%		65.00%
90 Days Delinquent	70.00%		70.00%		70.00%
Bankruptcy	60.00%		60.00%		60.00%
Foreclosure	80.00%		80.00%		80.00%
Projected Loss Assumptions, Base Case Expected Loss Estimates, First Lien RMBS [Abstract]
Period until intermediate CDR	48 months		48 months		48 months
Initial loss severity	65.00%	[1]	65.00%	[1]	65.00%	[1]
Final CPR(2)	15.00%	[1],[2]	15.00%	[1],[2]	15.00%	[1],[2]
First mortgage, subprime
Projected Loss Assumptions, First Lien Liquidation Rates [Abstract]
Current Loans Modified in Previous 12 Months	35.00%		35.00%		35.00%
30 – 59 Days Delinquent	45.00%		45.00%		45.00%
60 – 89 Days Delinquent	50.00%		50.00%		50.00%
90 Days Delinquent	60.00%		60.00%		60.00%
Bankruptcy	55.00%		55.00%		55.00%
Foreclosure	70.00%		70.00%		70.00%
Projected Loss Assumptions Text One [Abstract]
Period until which loss severity rate would continue (in months)			9 months
Projected Loss Assumptions, Base Case Expected Loss Estimates, First Lien RMBS [Abstract]
Period until intermediate CDR	48 months		48 months		48 months
Initial loss severity	90.00%	[1]	90.00%	[1]	90.00%	[1]
Final CPR(2)	15.00%	[1],[2]	15.00%	[1],[2]	15.00%	[1],[2]
RMBS
Projected Loss Assumptions Text One [Abstract]
Final conditional default rate as a percentage of plateau conditional default rate			5.00%
Prime first lien
Projected Loss Assumptions Text Two [Abstract]
Number of scenarios weighted in estimating expected losses			5
Minimum | Alt-A first lien
Projected Loss Assumptions, Base Case Expected Loss Estimates, First Lien RMBS [Abstract]
Plateau CDR	2.90%	[1]	2.10%	[1]	2.80%	[1]
Intermediate CDR	0.60%	[1]	0.40%	[1]	0.60%	[1]
Final CDR	0.10%	[1]	0.10%	[1]	0.10%	[1]
Initial conditional prepayment rate (CPR)	1.00%	[1]	0.00%	[1]	0.00%	[1]
Minimum | Option ARM
Projected Loss Assumptions, Base Case Expected Loss Estimates, First Lien RMBS [Abstract]
Plateau CDR	5.00%	[1]	3.90%	[1]	4.90%	[1]
Intermediate CDR	1.00%	[1]	0.80%	[1]	1.00%	[1]
Final CDR	0.20%	[1]	0.20%	[1]	0.20%	[1]
Initial conditional prepayment rate (CPR)	0.90%	[1]	1.00%	[1]	0.40%	[1]
Minimum | First mortgage, subprime
Projected Loss Assumptions, Base Case Expected Loss Estimates, First Lien RMBS [Abstract]
Plateau CDR	5.70%	[1]	5.30%	[1]	5.60%	[1]
Intermediate CDR	1.10%	[1]	1.10%	[1]	1.10%	[1]
Final CDR	0.30%	[1]	0.30%	[1]	0.30%	[1]
Initial conditional prepayment rate (CPR)	0.00%	[1]	0.00%	[1]	0.00%	[1]
Maximum | Alt-A first lien
Projected Loss Assumptions, Base Case Expected Loss Estimates, First Lien RMBS [Abstract]
Plateau CDR	16.80%	[1]	15.70%	[1]	18.40%	[1]
Intermediate CDR	3.40%	[1]	3.10%	[1]	3.70%	[1]
Final CDR	0.80%	[1]	0.80%	[1]	0.90%	[1]
Initial conditional prepayment rate (CPR)	23.20%	[1]	24.30%	[1]	34.20%	[1]
Maximum | Option ARM
Projected Loss Assumptions, Base Case Expected Loss Estimates, First Lien RMBS [Abstract]
Plateau CDR	15.80%	[1]	15.70%	[1]	16.80%	[1]
Intermediate CDR	3.20%	[1]	3.10%	[1]	3.40%	[1]
Final CDR	0.80%	[1]	0.80%	[1]	0.80%	[1]
Initial conditional prepayment rate (CPR)	9.00%	[1]	13.00%	[1]	13.10%	[1]
Maximum | First mortgage, subprime
Projected Loss Assumptions, Base Case Expected Loss Estimates, First Lien RMBS [Abstract]
Plateau CDR	16.50%	[1]	15.90%	[1]	16.20%	[1]
Intermediate CDR	3.30%	[1]	3.20%	[1]	3.20%	[1]
Final CDR	0.80%	[1]	0.80%	[1]	0.80%	[1]
Initial conditional prepayment rate (CPR)	13.70%	[1]	10.80%	[1]	15.70%	[1]
Weighted Average | Alt-A first lien
Projected Loss Assumptions, Base Case Expected Loss Estimates, First Lien RMBS [Abstract]
Plateau CDR	9.00%	[1]	8.50%	[1]	9.70%	[1]
Intermediate CDR	1.80%	[1]	1.70%	[1]	1.90%	[1]
Final CDR	0.40%	[1]	0.40%	[1]	0.50%	[1]
Initial conditional prepayment rate (CPR)	7.00%	[1]	7.00%	[1]	9.70%	[1]
Weighted Average | Option ARM
Projected Loss Assumptions, Base Case Expected Loss Estimates, First Lien RMBS [Abstract]
Plateau CDR	11.10%	[1]	10.70%	[1]	11.90%	[1]
Intermediate CDR	2.20%	[1]	2.10%	[1]	2.40%	[1]
Final CDR	0.50%	[1]	0.50%	[1]	0.50%	[1]
Initial conditional prepayment rate (CPR)	7.10%	[1]	7.10%	[1]	4.70%	[1]
Weighted Average | First mortgage, subprime
Projected Loss Assumptions, Base Case Expected Loss Estimates, First Lien RMBS [Abstract]
Plateau CDR	11.50%	[1]	11.20%	[1]	11.80%	[1]
Intermediate CDR	2.30%	[1]	2.20%	[1]	2.40%	[1]
Final CDR	0.40%	[1]	0.40%	[1]	0.40%	[1]
Initial conditional prepayment rate (CPR)	6.40%	[1]	6.50%	[1]	4.10%	[1]
Base Scenario | Total first lien
Projected Loss Assumptions Text One [Abstract]
Period for which estimated defaults are attributed to loans currently delinquent or in foreclosure			36 months
Assumed period for final conditional default rate to be reached			8 years 9 months
Period that final CDR was reached before assumption period end	3 months				3 months
Intermediate conditional default rate as a percentage of plateau conditional default rate			20.00%
Period of constant intermediate conditional default rate (in months)			36 months
Final conditional default rate as a percentage of plateau conditional default rate			5.00%
Loss severity (as a percent)			40.00%
Projected Loss Assumptions, Base Case Expected Loss Estimates, First Lien RMBS [Abstract]
Period until intermediate CDR			12 months
Somewhat Stressful Environment | Alt-A first lien
Projected Loss Assumptions Text Two [Abstract]
Increase in expected loss in case of increase in conditional default rate plateau period and loss severity recovery period			$ 30
Somewhat Stressful Environment | Total first lien
Projected Loss Assumptions Text Two [Abstract]
Increased final loss severity for subprime transactions used to calculate potential change in loss estimate (as a percent)			60.00%
Somewhat Stressful Environment | Option ARM
Projected Loss Assumptions Text Two [Abstract]
Increase in expected loss in case of increase in conditional default rate plateau period and loss severity recovery period			10
Somewhat Stressful Environment | First mortgage, subprime
Projected Loss Assumptions Text Two [Abstract]
Increase in expected loss in case of increase in conditional default rate plateau period and loss severity recovery period			73
Somewhat Stressful Environment | Prime first lien
Projected Loss Assumptions Text Two [Abstract]
Increase in the plateau period used to calculate potential change in loss estimate (in months)			6 months
Increased plateau period used to calculate potential change in loss estimate (in months)			42 months
Prior loss severity recovery period used to calculate potential change in loss estimate (in years)			4 years 6 months
Current loss severity recovery period used to calculate potential change in loss estimate (in years)			2 years 6 months
Increase in expected loss in case of increase in conditional default rate plateau period and loss severity recovery period			4
Least Stressful Environment | Alt-A first lien
Projected Loss Assumptions Text Two [Abstract]
Decrease in expected loss in case of decrease in conditional default rate plateau period			26
Least Stressful Environment | Option ARM
Projected Loss Assumptions Text Two [Abstract]
Decrease in expected loss in case of decrease in conditional default rate plateau period			25
Least Stressful Environment | First mortgage, subprime
Projected Loss Assumptions Text Two [Abstract]
Decrease in expected loss in case of decrease in conditional default rate plateau period			65
Least Stressful Environment | Prime first lien
Projected Loss Assumptions Text Two [Abstract]
Period of decrease in conditional default rate until final rate is achieved (in months)			9 months
Decrease in expected loss in case of decrease in conditional default rate plateau period			5
Somewhat Less Stressful Environment | Alt-A first lien
Projected Loss Assumptions Text Two [Abstract]
Decrease in expected loss in case of less gradual conditional default rate recovery and changes in initial subprime loss severity rate			0
Somewhat Less Stressful Environment | Total first lien
Projected Loss Assumptions Text One [Abstract]
Period from initial to final conditional prepayment rate (in months)			18 months
Projected Loss Assumptions Text Two [Abstract]
Current loss severity recovery period used to calculate potential change in loss estimate (in years)			2 years 6 months
Initial subprime loss severity rate assumed for 12 months (as a percent)			80.00%
Initial subprime loss severity rate assumed to be recovered over two years (as a percent)			40.00%
Somewhat Less Stressful Environment | Option ARM
Projected Loss Assumptions Text Two [Abstract]
Decrease in expected loss in case of less gradual conditional default rate recovery and changes in initial subprime loss severity rate			10
Somewhat Less Stressful Environment | First mortgage, subprime
Projected Loss Assumptions Text Two [Abstract]
Decrease in expected loss in case of less gradual conditional default rate recovery and changes in initial subprime loss severity rate			23
Somewhat Less Stressful Environment | Prime first lien
Projected Loss Assumptions Text Two [Abstract]
Decrease in expected loss in case of less gradual conditional default rate recovery and changes in initial subprime loss severity rate			1
More Stressful Environment | Alt-A first lien
Projected Loss Assumptions Text Two [Abstract]
Increase in expected loss in case of increase in loss severity recovery period in an even more stressful scenario			83
More Stressful Environment | Option ARM
Projected Loss Assumptions Text Two [Abstract]
Increase in expected loss in case of increase in loss severity recovery period in an even more stressful scenario			23
More Stressful Environment | First mortgage, subprime
Projected Loss Assumptions Text Two [Abstract]
Increase in expected loss in case of increase in loss severity recovery period in an even more stressful scenario			107
More Stressful Environment | Prime first lien
Projected Loss Assumptions Text Two [Abstract]
Period of decrease in conditional default rate until final rate is achieved (in months)			15 months
Increase in expected loss in case of increase in loss severity recovery period in an even more stressful scenario			$ 10

[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.