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, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Residential Non-Agency Prime [Member] | Residential [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance	$ 547	$ 713	$ 624	$ 803
Net Gains (Losses) Included in Net Income	(2)	(4)	(6)	(5)
Net Gains (Losses) Included in Other Comprehensive Income (Loss)	(4)	23	4	60
Purchases
Sales		(61)		(109)
Principal Payments	(41)	(40)	(122)	(118)
Issuances
Settlements
End of Period Balance	500	631	500	631
Net Change in Unrealized Gains (Losses) Relating to Assets Still Held at End of Period	(4)	26	4	58
Residential Non-Agency Non-Prime [Member] | Residential [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance	319	796	355	802
Net Gains (Losses) Included in Net Income	(3)	(8)	(11)	(18)
Net Gains (Losses) Included in Other Comprehensive Income (Loss)	(4)	132	13	197
Purchases
Sales		(562)	(20)	(562)
Principal Payments	(9)	(18)	(34)	(79)
Issuances
Settlements
End of Period Balance	303	340	303	340
Net Change in Unrealized Gains (Losses) Relating to Assets Still Held at End of Period	(4)	23	14	52
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	40	112	15	117
Net Gains (Losses) Included in Net Income	1	1	2	7
Net Gains (Losses) Included in Other Comprehensive Income (Loss)	(2)	(4)	(1)
Purchases	3	3	28	3
Sales		(93)		(93)
Principal Payments	(2)	(3)	(4)	(18)
Issuances
Settlements
End of Period Balance	40	16	40	16
Net Change in Unrealized Gains (Losses) Relating to Assets Still Held at End of Period	(2)	2	(1)	2
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 Still Held at End of Period
Available-for-Sale Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance	915	1,769	1,003	1,893
Net Gains (Losses) Included in Net Income	(4)	(9)	(15)	(3)
Net Gains (Losses) Included in Other Comprehensive Income (Loss)	(10)	146	16	249
Purchases	3	3	28	3
Sales		(851)	(20)	(906)
Principal Payments	(52)	(62)	(160)	(240)
Issuances
Settlements
End of Period Balance	852	996	852	996
Net Change in Unrealized Gains (Losses) Relating to Assets Still Held at End of Period	(10)	51	17	112
Mortgage servicing rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance	2,377	1,594	1,700	1,519
Net Gains (Losses) Included in Net Income	11	(275)	196	(705)
Net Gains (Losses) Included in Other Comprehensive Income (Loss)
Purchases	2	10	7	39
Sales
Principal Payments
Issuances	187	224	674	700
Settlements
End of Period Balance	2,577	1,553	2,577	1,553
Net Change in Unrealized Gains (Losses) Relating to Assets Still Held at End of Period	11	(275)	196	(705)
Commercial Non-Agency Mortgage-Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance		37		42
Net Gains (Losses) Included in Net Income				1
Net Gains (Losses) Included in Other Comprehensive Income (Loss)		2
Sales		(39)		(39)
Principal Payments				(4)
Net Change in Unrealized Gains (Losses) Relating to Assets Still Held at End of Period
Collateralized Loan Obligations [Member] | Asset-Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance		102		120
Net Gains (Losses) Included in Net Income		2		12
Net Gains (Losses) Included in Other Comprehensive Income (Loss)		(7)		(8)
Sales		(96)		(103)
Principal Payments		(1)		(21)
Net Change in Unrealized Gains (Losses) Relating to Assets Still Held at End of Period
Derivative [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance	423	1,360	1,179	1,228
Net Gains (Losses) Included in Net Income	182	843	(34)	2,050
Net Gains (Losses) Included in Other Comprehensive Income (Loss)
Purchases		1	1	1
Sales	(2)	(1)	(4)	(3)
Principal Payments
Issuances
Settlements	14	(713)	(525)	(1,786)
End of Period Balance	617	1,490	617	1,490
Net Change in Unrealized Gains (Losses) Relating to Assets Still Held at End of Period	$ 62	$ (557)	$ (565)	$ (1,407)