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										3 Months Ended
	Mar. 31, 2013 Residential Non-agency Prime [Member] Residential [Member]	Mar. 31, 2012 Residential Non-agency Prime [Member] Residential [Member]	Mar. 31, 2013 Residential Non-agency Non-prime [Member] Residential [Member]	Mar. 31, 2012 Residential Non-agency Non-prime [Member] Residential [Member]	Mar. 31, 2013 Asset Backed Securities Other [Member] Asset-Backed Securities [Member]	Mar. 31, 2012 Asset Backed Securities Other [Member] Asset-Backed Securities [Member]	Mar. 31, 2013 Corporate debt securities [Member]	Dec. 31, 2012 Corporate debt securities [Member]	Mar. 31, 2012 Corporate debt securities [Member]	Dec. 31, 2011 Corporate debt securities [Member]	Mar. 31, 2013 Available - for - sale securities [Member]	Mar. 31, 2012 Available - for - sale securities [Member]	Mar. 31, 2013 Mortgage servicing rights [Member]	Mar. 31, 2012 Mortgage servicing rights [Member]	Mar. 31, 2013 Net derivative assets and liabilities [Member]	Mar. 31, 2012 Net derivative assets and liabilities [Member]	Mar. 31, 2012 Commercial Non-Agency Mortgage-Backed Securities [Member]	Mar. 31, 2012 Collateralized Loan Obligations [Member] Asset-Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance	$ 624	$ 803	$ 355	$ 802	$ 15	$ 117	$ 9	$ 9	$ 9	$ 9	$ 1,003	$ 1,893	$ 1,700	$ 1,519	$ 1,179	$ 1,228	$ 42	$ 120
Net Gains (Losses) Included in Net Income	(2)		(7)	(3)	1	3					(8)	5	(1)	(56)	147	331		5
Net Gains (Losses) Included in Other Comprehensive Income (Loss)	11	16	14	37		1					25	53						(1)
Purchases					25						25		2	13	1
Sales		(48)										(48)			(1)
Principal Payments	(34)	(38)	(12)	(30)	(1)	(9)					(47)	(84)					(2)	(5)
Issuances													254	261
Settlements															(340)	(470)
End of Period Balance	599	733	350	806	40	112	9	9	9	9	998	1,819	1,955	1,737	986	1,089	40	119
Net Change in Unrealized Gains (Losses) Relating to Assets Still Held at End of Period	$ 11	$ 13	$ 14	$ 37		$ 1					$ 25	$ 50	$ (1)	$ (56)	$ (338)	$ (461)		$ (1)