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		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 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	$ 447	$ 547	$ 478	$ 624
Net Gains (Losses) Included in Net Income		(2)		(6)
Net Gains (Losses) Included in Other Comprehensive Income (Loss)	2	(4)	14	4
Purchases
Sales
Principal Payments	(23)	(41)	(66)	(122)
Issuances
Settlements
End of Period Balance	426	500	426	500
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Still Held at End of Period	2	(4)	14	4
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	286	319	297	355
Net Gains (Losses) Included in Net Income		(3)	(4)	(11)
Net Gains (Losses) Included in Other Comprehensive Income (Loss)	6	(4)	14	13
Purchases
Sales				(20)
Principal Payments	(8)	(9)	(23)	(34)
Issuances
Settlements
End of Period Balance	284	303	284	303
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Still Held at End of Period	6	(4)	14	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	66	40	63	15
Net Gains (Losses) Included in Net Income		1	2	2
Net Gains (Losses) Included in Other Comprehensive Income (Loss)		(2)	1	(1)
Purchases		3	4	28
Sales
Principal Payments	(2)	(2)	(6)	(4)
Issuances
Settlements
End of Period Balance	64	40	64	40
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Still Held at End of Period		(2)	1	(1)
Corporate debt securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance	9	9	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	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	2,412	2,377	2,680	1,700
Net Gains (Losses) Included in Net Income	(61)	11	(345)	196
Net Gains (Losses) Included in Other Comprehensive Income (Loss)
Purchases	1	2	3	7
Sales			(141)
Principal Payments
Issuances	109	187	264	674
Settlements
End of Period Balance	2,461	2,577	2,461	2,577
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Still Held at End of Period	(61)	11	(345)	196
Derivative [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance	558	423	445	1,179
Net Gains (Losses) Included in Net Income	95	182	568	(34)
Net Gains (Losses) Included in Other Comprehensive Income (Loss)
Purchases			1	1
Sales	(1)	(2)	(1)	(4)
Principal Payments
Issuances
Settlements	(187)	14	(548)	(525)
End of Period Balance	465	617	465	617
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Still Held at End of Period	(15)	55	80	(218)
Available-for-Sale Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance	808	915	847	1,003
Net Gains (Losses) Included in Net Income		(4)	(2)	(15)
Net Gains (Losses) Included in Other Comprehensive Income (Loss)	8	(10)	29	16
Purchases		3	4	28
Sales				(20)
Principal Payments	(33)	(52)	(95)	(160)
Issuances
Settlements
End of Period Balance	783	852	783	852
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Still Held at End of Period	$ 8	$ (10)	$ 29	$ 17