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		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 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	$ 465	$ 599	$ 478	$ 624
Net Gains (Losses) Included in Net Income		(2)		(4)
Net Gains (Losses) Included in Other Comprehensive Income (Loss)	5	(3)	12	8
Purchases
Sales
Principal Payments	(23)	(47)	(43)	(81)
Issuances
Settlements
End of Period Balance	447	547	447	547
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Still Held at End of Period	5	(3)	12	8
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	350	297	355
Net Gains (Losses) Included in Net Income	(3)	(1)	(4)	(8)
Net Gains (Losses) Included in Other Comprehensive Income (Loss)	1	3	8	17
Purchases
Sales		(20)		(20)
Principal Payments	(9)	(13)	(15)	(25)
Issuances
Settlements
End of Period Balance	286	319	286	319
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Still Held at End of Period		5	7	18
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	65	40	63	15
Net Gains (Losses) Included in Net Income	1		2	1
Net Gains (Losses) Included in Other Comprehensive Income (Loss)		1	1	1
Purchases	2		4	25
Sales
Principal Payments	(2)	(1)	(4)	(2)
Issuances
Settlements
End of Period Balance	66	40	66	40
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Still Held at End of Period		1	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	2,618	1,955	2,680	1,700
Net Gains (Losses) Included in Net Income	(137)	186	(284)	185
Net Gains (Losses) Included in Other Comprehensive Income (Loss)
Purchases	1	3	2	5
Sales	(141)		(141)
Principal Payments
Issuances	71	233	155	487
Settlements
End of Period Balance	2,412	2,377	2,412	2,377
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Still Held at End of Period	(137)	186	(284)	185
Derivative [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance	482	986	445	1,179
Net Gains (Losses) Included in Net Income	288	(363)	473	(216)
Net Gains (Losses) Included in Other Comprehensive Income (Loss)
Purchases			1	1
Sales		(1)		(2)
Principal Payments
Issuances
Settlements	(212)	(199)	(361)	(539)
End of Period Balance	558	423	558	423
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Still Held at End of Period	123	(286)	161	(374)
Available-for-Sale Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance	836	998	847	1,003
Net Gains (Losses) Included in Net Income	(2)	(3)	(2)	(11)
Net Gains (Losses) Included in Other Comprehensive Income (Loss)	6	1	21	26
Purchases	2		4	25
Sales		(20)		(20)
Principal Payments	(34)	(61)	(62)	(108)
Issuances
Settlements
End of Period Balance	808	915	808	915
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Still Held at End of Period	$ 5	$ 3	$ 20	$ 27