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, 2015	Mar. 31, 2014
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	$ 405	$ 478
Net Gains (Losses) Included in Net Income
Net Gains (Losses) Included in Other Comprehensive Income (Loss)	(1)	7
Purchases
Sales
Principal Payments	(19)	(20)
Issuances
Settlements
End of Period Balance	385	465
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Still Held at End of Period	(1)	7
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	280	297
Net Gains (Losses) Included in Net Income		(1)
Net Gains (Losses) Included in Other Comprehensive Income (Loss)		7
Purchases
Sales
Principal Payments	(7)	(6)
Issuances
Settlements
End of Period Balance	273	297
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Still Held at End of Period		7
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	62	63
Net Gains (Losses) Included in Net Income	1	1
Net Gains (Losses) Included in Other Comprehensive Income (Loss)	2	1
Purchases		2
Sales
Principal Payments	(4)	(2)
Issuances
Settlements
End of Period Balance	61	65
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Still Held at End of Period	2	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	2,338	2,680
Net Gains (Losses) Included in Net Income	(239)	(147)
Net Gains (Losses) Included in Other Comprehensive Income (Loss)
Purchases	6	1
Sales
Principal Payments
Issuances	145	84
Settlements
End of Period Balance	2,250	2,618
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Still Held at End of Period	(239)	(147)
Derivative [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance	574	445
Net Gains (Losses) Included in Net Income	371	185
Net Gains (Losses) Included in Other Comprehensive Income (Loss)
Purchases		1
Sales	(1)
Principal Payments
Issuances
Settlements	(215)	(149)
End of Period Balance	729	482
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Still Held at End of Period	243	60
Available-for-Sale Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance	756	847
Net Gains (Losses) Included in Net Income	1
Net Gains (Losses) Included in Other Comprehensive Income (Loss)	1	15
Purchases		2
Sales
Principal Payments	(30)	(28)
Issuances
Settlements
End of Period Balance	728	836
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Still Held at End of Period	$ 1	$ 15