Fair Values of Assets and Liabilities - Changes in Fair Value for All Assets and Liabilities Measured at Fair Value on Recurring Basis Using Significant Unobservable Inputs (Level 3) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Non-agency Prime [Member] | Mortgage-backed securities Residential [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance	$ 478	$ 624
Net Gains (Losses) Included in Net Income		(2)
Net Gains (Losses) Included in Other Comprehensive Income (Loss)	7	11
Purchases
Sales
Principal Payments	(20)	(34)
Issuances
Settlements
End of Period Balance	465	599
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Still Held at End of Period	7	11
Non-agency Non-prime [Member] | Mortgage-backed securities Residential [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance	297	355
Net Gains (Losses) Included in Net Income	(1)	(7)
Net Gains (Losses) Included in Other Comprehensive Income (Loss)	7	14
Purchases
Sales
Principal Payments	(6)	(12)
Issuances
Settlements
End of Period Balance	297	350
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Still Held at End of Period	7	14
Asset-backed securities Other [Member] | Asset-Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance	63	15
Net Gains (Losses) Included in Net Income	1	1
Net Gains (Losses) Included in Other Comprehensive Income (Loss)	1
Purchases	2	25
Sales
Principal Payments	(2)	(1)
Issuances
Settlements
End of Period Balance	65	40
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Still Held at End of Period	1
Corporate debt securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance	9	9
Net Gains (Losses) Included in Net Income
Net Gains (Losses) Included in Other Comprehensive Income (Loss)
Purchases
Sales
Principal Payments
Issuances
Settlements
End of Period Balance	9	9
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Still Held at End of Period
Mortgage servicing rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance	2,680	1,700
Net Gains (Losses) Included in Net Income	(147)	(1)
Net Gains (Losses) Included in Other Comprehensive Income (Loss)
Purchases	1	2
Sales
Principal Payments
Issuances	84	254
Settlements
End of Period Balance	2,618	1,955
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Still Held at End of Period	(147)	(1)
Derivative [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance	445	1,179
Net Gains (Losses) Included in Net Income	185	147
Net Gains (Losses) Included in Other Comprehensive Income (Loss)
Purchases	1	1
Sales		(1)
Principal Payments
Issuances
Settlements	(149)	(340)
End of Period Balance	482	986
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Still Held at End of Period	60	71
Available-for-Sale Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance	847	1,003
Net Gains (Losses) Included in Net Income		(8)
Net Gains (Losses) Included in Other Comprehensive Income (Loss)	15	25
Purchases	2	25
Sales
Principal Payments	(28)	(47)
Issuances
Settlements
End of Period Balance	836	998
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Still Held at End of Period	$ 15	$ 25