Expected Losses to be Paid - Key Assumptions in Base Case Expected Loss Estimates Second Lien RMBS (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended		9 Months Ended		12 Months Ended
	Jun. 30, 2014		Sep. 30, 2014		Dec. 31, 2013
Guarantor Obligations [Line Items]
Increase in expected losses due to increased default of loans reaching their amortization period and increased recoveries			$ 36
Loss estimate sensitivity analysis increase in CDR ramp down period			5 months
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
Guarantor Obligations [Line Items]
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]
Alt-A first lien | Minimum
Guarantor Obligations [Line Items]
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]
Alt-A first lien | Maximum
Guarantor Obligations [Line Items]
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]
Alt-A first lien | Weighted Average
Guarantor Obligations [Line Items]
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]
Second lien
Guarantor Obligations [Line Items]
Final CPR(2)			10.00%
Typical past due period for loans to be charged off (in days)			180 days
Period of default estimate			5 months
Number of preceding months liquidation rates used to estimate loan default rate			12 months
Number of months the conditional default rate is calculated applying liquidation rates to current period past due balances excluding 30 to 59 days past due			4 months
Period of decrease in conditional default rate until final rate is achieved (in months)			28 months
Stress period (in months)			34 months
Number of monthly delinquency categories			5 months
Period of constant conditional default rate (in months)			1 month
Loss recovery assumption	2.00%		10.00%		2.00%
Conditional prepayment rate base case average number of months			3 months
Number of conditional default rate curves modeled in estimating losses			3
Second lien | Minimum
Guarantor Obligations [Line Items]
First delinquency category (in days)			30 days
Second delinquency category (in days)			60 days
Third delinquency category (in days)			90 days
Fourth delinquency category (in days)			120 days
Fifth delinquency category (in days)			150 days
Second lien | Maximum
Guarantor Obligations [Line Items]
First delinquency category (in days)			59 days
Second delinquency category (in days)			89 days
Third delinquency category (in days)			119 days
Fourth delinquency category (in days)			149 days
Fifth delinquency category (in days)			179 days
Close ended second lien
Guarantor Obligations [Line Items]
Initial loss severity	98.00%	[1]	98.00%	[1]	98.00%	[1]
Final CPR(2)	10.00%	[1],[2]	10.00%	[1],[2]	10.00%	[1],[2]
Expected period until final conditional default rate (in months)	34 months		34 months		34 months
Close ended second lien | Minimum
Guarantor Obligations [Line Items]
Plateau CDR	4.80%	[1]	6.80%	[1]	7.30%	[1]
Final CDR	3.50%	[1]	3.50%	[1]	3.50%	[1]
Initial conditional prepayment rate (CPR)	2.60%	[1]	3.00%	[1]	3.10%	[1]
Close ended second lien | Maximum
Guarantor Obligations [Line Items]
Plateau CDR	14.90%	[1]	15.10%	[1]	15.10%	[1]
Final CDR	9.10%	[1]	9.10%	[1]	9.10%	[1]
Initial conditional prepayment rate (CPR)	10.40%	[1]	11.40%	[1]	12.00%	[1]
Close ended second lien | Weighted Average
Guarantor Obligations [Line Items]
Plateau CDR	7.70%	[1]	7.70%	[1]	8.50%	[1]
Final CDR	5.00%	[1]	4.90%	[1]	5.00%	[1]
Initial conditional prepayment rate (CPR)	8.40%	[1]	9.20%	[1]	7.10%	[1]
HELOCs
Guarantor Obligations [Line Items]
Initial loss severity	98.00%	[1]			98.00%	[1]
Final CPR(2)	10.00%	[1],[2]	10.00%	[1],[2]	10.00%	[1],[2]
Expected period until final conditional default rate (in months)	34 months		34 months		34 months
Initial period for which borrower can pay only interest payments			10 years
Loans reaching amortization period that will default, percentage of default			7.50%
HELOCs | Minimum
Guarantor Obligations [Line Items]
Plateau CDR	2.20%	[1]	2.80%	[1]	2.30%	[1]
Final CDR	0.50%	[1]	0.50%	[1]	0.40%	[1]
Initial loss severity			90.00%	[1]
Initial conditional prepayment rate (CPR)	2.40%	[1]	5.10%	[1]	2.70%	[1]
HELOCs | Maximum
Guarantor Obligations [Line Items]
Plateau CDR	9.60%	[1]	8.50%	[1]	7.70%	[1]
Final CDR	3.20%	[1]	3.20%	[1]	3.20%	[1]
Initial loss severity			98.00%	[1]
Initial conditional prepayment rate (CPR)	19.40%	[1]	16.00%	[1]	21.50%	[1]
HELOCs | Weighted Average
Guarantor Obligations [Line Items]
Plateau CDR	4.30%	[1]	4.20%	[1]	4.90%	[1]
Final CDR	1.20%	[1]	1.20%	[1]	1.10%	[1]
Initial loss severity			91.50%	[1]
Initial conditional prepayment rate (CPR)	9.30%	[1]	10.30%	[1]	9.90%	[1]
Option ARM
Guarantor Obligations [Line Items]
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]
Option ARM | Minimum
Guarantor Obligations [Line Items]
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]
Option ARM | Maximum
Guarantor Obligations [Line Items]
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]
Option ARM | Weighted Average
Guarantor Obligations [Line Items]
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]
Subprime
Guarantor Obligations [Line Items]
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]
Period until which loss severity rate would continue (in months)			9 months
Subprime | Minimum
Guarantor Obligations [Line Items]
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]
Subprime | Maximum
Guarantor Obligations [Line Items]
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]
Subprime | Weighted Average
Guarantor Obligations [Line Items]
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 | Second lien
Guarantor Obligations [Line Items]
Period of decrease in conditional default rate until final rate is achieved (in months)			28 months
Stress period (in months)			34 months
Period of constant conditional default rate (in months)			1 month
Scenario 1 | Second lien
Guarantor Obligations [Line Items]
Period of decrease in conditional default rate until final rate is achieved (in months)			33 months
Stress period (in months)			42 months
Increased plateau period used to calculate potential change in loss estimate (in months)			4 months
Scenario 1 | Close ended second lien
Guarantor Obligations [Line Items]
Loss estimate sensitivity analysis change in estimate for increased CDR plateau period			2
Scenario 1 | HELOCs
Guarantor Obligations [Line Items]
Loss estimate sensitivity analysis change in estimate for increased CDR plateau period			17
Scenario 2 | Second lien
Guarantor Obligations [Line Items]
Stress period (in months)			24 months
Period of constant conditional default rate (in months)			1 month
Decreased ramp down period used to calculate potential change in loss estimate (in months)			18 months
Scenario 2 | Close ended second lien
Guarantor Obligations [Line Items]
Loss estimate sensitivity analysis change in estimate for decreased CDR ramp down period			2
Scenario 2 | HELOCs
Guarantor Obligations [Line Items]
Loss estimate sensitivity analysis change in estimate for decreased CDR ramp down period			$ 17

[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.