Expected Losses to be Paid - First Lien Liquidation Rates (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended			12 Months Ended
	Mar. 31, 2014		Dec. 31, 2012	Dec. 31, 2013
Guarantor Obligations [Line Items]
Period from initial to final conditional prepayment rate (in months)				2 years 6 months
Liquidation rate for real estate owned (as a percent)	100.00%			100.00%
Period until which loss severity rate would continue (in months)				18 months
Alt-A first lien
Guarantor Obligations [Line Items]
Period from plateau to intermediate conditional default rate (in months)	48 months			48 months
Loss severity (as a percent)	65.00%	[1]		65.00%	[1]
Final conditional prepayment rate (as a percent)	15.00%	[1]		15.00%	[1]
Total first lien
Guarantor Obligations [Line Items]
Period from initial to final conditional prepayment rate (in months)	12 months
Current conditional prepayment rate used in alternate scenario for loss estimate (as a percent)	15.00%
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%
Loss severity recovery period used to calculate potential change in loss estimate in even more stressful scenario (in years)	9 years
Number of scenarios where the recovery was faster than in base case	2
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
Guarantor Obligations [Line Items]
Liquidation rate for current loans modified in previous 12 months (as a percent)	35.00%			35.00%
Liquidation rate for 30 - 59 days delinquent category (as a percent)	50.00%			50.00%
Liquidation rate for 60 - 89 days delinquent category (as a percent)	60.00%			60.00%
Liquidation rate for 90 days delinquent category (as a percent)	75.00%			75.00%
Liquidation rate for bankruptcy delinquent category (as a percent)	60.00%			60.00%
Liquidation rate for foreclosure category (as a percent)	85.00%			85.00%
Option ARM
Guarantor Obligations [Line Items]
Liquidation rate for current loans modified in previous 12 months (as a percent)	35.00%			35.00%
Liquidation rate for 30 - 59 days delinquent category (as a percent)	50.00%			50.00%
Liquidation rate for 60 - 89 days delinquent category (as a percent)	65.00%			65.00%
Liquidation rate for 90 days delinquent category (as a percent)	70.00%			70.00%
Liquidation rate for bankruptcy delinquent category (as a percent)	60.00%			60.00%
Liquidation rate for foreclosure category (as a percent)	80.00%			80.00%
Period from plateau to intermediate conditional default rate (in months)	48 months			48 months
Loss severity (as a percent)	65.00%	[1]		65.00%	[1]
Final conditional prepayment rate (as a percent)	15.00%	[1]		15.00%	[1]
First mortgage, subprime
Guarantor Obligations [Line Items]
Liquidation rate for current loans modified in previous 12 months (as a percent)	35.00%			35.00%
Liquidation rate for 30 - 59 days delinquent category (as a percent)	45.00%			45.00%
Liquidation rate for 60 - 89 days delinquent category (as a percent)	50.00%			50.00%
Liquidation rate for 90 days delinquent category (as a percent)	60.00%			60.00%
Liquidation rate for bankruptcy delinquent category (as a percent)	55.00%			55.00%
Liquidation rate for foreclosure category (as a percent)	70.00%			70.00%
Period from plateau to intermediate conditional default rate (in months)	48 months			48 months
Period until which loss severity rate would continue (in months)			9 months	9 months
Loss severity (as a percent)	90.00%	[1]		90.00%	[1]
Final conditional prepayment rate (as a percent)	15.00%	[1]		15.00%	[1]
RMBS
Guarantor Obligations [Line Items]
Intermediate Conditional Default Rate	5.00%
Residential, Prime, Financing Receivable [Member]
Guarantor Obligations [Line Items]
Number of scenarios weighted in estimating expected losses	5
Minimum | Alt-A first lien
Guarantor Obligations [Line Items]
Plateau conditional default rate (as a percent)	2.30%	[1]		2.80%	[1]
Intermediate Conditional Default Rate	0.50%	[1]		0.60%	[1]
Final conditional default rate trended down to (as a percent)	0.10%	[1]		0.10%	[1]
Initial conditional prepayment rate (as a percent)	0.90%	[1]		0.00%	[1]
Minimum | Option ARM
Guarantor Obligations [Line Items]
Plateau conditional default rate (as a percent)	3.80%	[1]		4.90%	[1]
Intermediate Conditional Default Rate	0.80%	[1]		1.00%	[1]
Final conditional default rate trended down to (as a percent)	0.20%	[1]		0.20%	[1]
Initial conditional prepayment rate (as a percent)	0.80%	[1]		0.40%	[1]
Minimum | First mortgage, subprime
Guarantor Obligations [Line Items]
Plateau conditional default rate (as a percent)	5.90%	[1]		5.60%	[1]
Intermediate Conditional Default Rate	1.20%	[1]		1.10%	[1]
Final conditional default rate trended down to (as a percent)	0.30%	[1]		0.30%	[1]
Initial conditional prepayment rate (as a percent)	0.00%	[1]		0.00%	[1]
Maximum | Alt-A first lien
Guarantor Obligations [Line Items]
Plateau conditional default rate (as a percent)	18.40%	[1]		18.40%	[1]
Intermediate Conditional Default Rate	3.70%	[1]		3.70%	[1]
Final conditional default rate trended down to (as a percent)	0.90%	[1]		0.90%	[1]
Initial conditional prepayment rate (as a percent)	33.90%	[1]		34.20%	[1]
Maximum | Option ARM
Guarantor Obligations [Line Items]
Plateau conditional default rate (as a percent)	16.80%	[1]		16.80%	[1]
Intermediate Conditional Default Rate	3.40%	[1]		3.40%	[1]
Final conditional default rate trended down to (as a percent)	0.80%	[1]		0.80%	[1]
Initial conditional prepayment rate (as a percent)	12.20%	[1]		13.10%	[1]
Maximum | First mortgage, subprime
Guarantor Obligations [Line Items]
Plateau conditional default rate (as a percent)	16.30%	[1]		16.20%	[1]
Intermediate Conditional Default Rate	3.30%	[1]		3.20%	[1]
Final conditional default rate trended down to (as a percent)	0.80%	[1]		0.80%	[1]
Initial conditional prepayment rate (as a percent)	11.60%	[1]		15.70%	[1]
Base Scenario | Total first lien
Guarantor Obligations [Line Items]
Period for which estimated defaults are attributed to loans currently delinquent or in foreclosure	36 months
Period from plateau to intermediate conditional default rate (in months)	12 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%
Somewhat Stressful Environment [Member] | Alt-A first lien
Guarantor Obligations [Line Items]
Increase in expected loss in case of increase in conditional default rate plateau period and loss severity recovery period	$ 39
Somewhat Stressful Environment [Member] | Total first lien
Guarantor Obligations [Line Items]
Increased final loss severity for subprime transactions used to calculate potential change in loss estimate (as a percent)	60.00%
Somewhat Stressful Environment [Member] | Option ARM
Guarantor Obligations [Line Items]
Increase in expected loss in case of increase in conditional default rate plateau period and loss severity recovery period	13
Somewhat Stressful Environment [Member] | First mortgage, subprime
Guarantor Obligations [Line Items]
Increase in expected loss in case of increase in conditional default rate plateau period and loss severity recovery period	93
Somewhat Stressful Environment [Member] | Residential, Prime, Financing Receivable [Member]
Guarantor Obligations [Line Items]
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 [Member] | Alt-A first lien
Guarantor Obligations [Line Items]
Decrease in expected loss in case of decrease in conditional default rate plateau period	36
Least Stressful Environment [Member] | Option ARM
Guarantor Obligations [Line Items]
Decrease in expected loss in case of decrease in conditional default rate plateau period	28
Least Stressful Environment [Member] | First mortgage, subprime
Guarantor Obligations [Line Items]
Decrease in expected loss in case of decrease in conditional default rate plateau period	78
Least Stressful Environment [Member] | Residential, Prime, Financing Receivable [Member]
Guarantor Obligations [Line Items]
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	4
Somewhat Less Stressful Environment [Member] | Alt-A first lien
Guarantor Obligations [Line Items]
Decrease in expected loss in case of less gradual conditional default rate recovery and changes in initial subprime loss severity rate	1
Somewhat Less Stressful Environment [Member] | Total first lien
Guarantor Obligations [Line Items]
Period from initial to final conditional prepayment rate (in months)	18 months
Initial subprime loss severity rate assumed to be recovered over two years (as a percent)	40.00%
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%
Somewhat Less Stressful Environment [Member] | Option ARM
Guarantor Obligations [Line Items]
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 [Member] | First mortgage, subprime
Guarantor Obligations [Line Items]
Decrease in expected loss in case of less gradual conditional default rate recovery and changes in initial subprime loss severity rate	25
Somewhat Less Stressful Environment [Member] | Residential, Prime, Financing Receivable [Member]
Guarantor Obligations [Line Items]
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 [Member] | Alt-A first lien
Guarantor Obligations [Line Items]
Increase in expected loss in case of increase in loss severity recovery period in an even more stressful scenario	104
More Stressful Environment [Member] | Option ARM
Guarantor Obligations [Line Items]
Increase in expected loss in case of increase in loss severity recovery period in an even more stressful scenario	31
More Stressful Environment [Member] | First mortgage, subprime
Guarantor Obligations [Line Items]
Increase in expected loss in case of increase in loss severity recovery period in an even more stressful scenario	138
More Stressful Environment [Member] | Residential, Prime, Financing Receivable [Member]
Guarantor Obligations [Line Items]
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	$ 11

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