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		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended								3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended	6 Months Ended	3 Months Ended	6 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2013 Residential Non-Agency Prime [Member] Residential [Member]	Jun. 30, 2012 Residential Non-Agency Prime [Member] Residential [Member]	Jun. 30, 2013 Residential Non-Agency Prime [Member] Residential [Member]	Jun. 30, 2012 Residential Non-Agency Prime [Member] Residential [Member]	Jun. 30, 2013 Residential Non-Agency Non-Prime [Member] Residential [Member]	Jun. 30, 2012 Residential Non-Agency Non-Prime [Member] Residential [Member]	Jun. 30, 2013 Residential Non-Agency Non-Prime [Member] Residential [Member]	Jun. 30, 2012 Residential Non-Agency Non-Prime [Member] Residential [Member]	Jun. 30, 2013 Asset Backed Securities Other [Member] Asset-Backed Securities [Member]	Jun. 30, 2012 Asset Backed Securities Other [Member] Asset-Backed Securities [Member]	Jun. 30, 2013 Asset Backed Securities Other [Member] Asset-Backed Securities [Member]	Jun. 30, 2012 Asset Backed Securities Other [Member] Asset-Backed Securities [Member]	Jun. 30, 2013 Corporate debt securities [Member]	Mar. 31, 2013 Corporate debt securities [Member]	Dec. 31, 2012 Corporate debt securities [Member]	Jun. 30, 2012 Corporate debt securities [Member]	Mar. 31, 2012 Corporate debt securities [Member]	Dec. 31, 2011 Corporate debt securities [Member]	Jun. 30, 2013 Available-for-Sale Securities [Member]	Jun. 30, 2012 Available-for-Sale Securities [Member]	Jun. 30, 2013 Available-for-Sale Securities [Member]	Jun. 30, 2012 Available-for-Sale Securities [Member]	Jun. 30, 2013 Mortgage servicing rights [Member]	Jun. 30, 2012 Mortgage servicing rights [Member]	Jun. 30, 2013 Mortgage servicing rights [Member]	Jun. 30, 2012 Mortgage servicing rights [Member]	Jun. 30, 2012 Commercial Non-Agency Mortgage-Backed Securities [Member]	Jun. 30, 2012 Commercial Non-Agency Mortgage-Backed Securities [Member]	Jun. 30, 2012 Collateralized Loan Obligations [Member] Asset-Backed Securities [Member]	Jun. 30, 2012 Collateralized Loan Obligations [Member] Asset-Backed Securities [Member]	Jun. 30, 2013 Derivative [Member]	Jun. 30, 2012 Derivative [Member]	Jun. 30, 2013 Derivative [Member]	Jun. 30, 2012 Derivative [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance	$ 599	$ 733	$ 624	$ 803	$ 350	$ 806	$ 355	$ 802	$ 40	$ 112	$ 15	$ 117	$ 9	$ 9	$ 9	$ 9	$ 9	$ 9	$ 998	$ 1,819	$ 1,003	$ 1,893	$ 1,955	$ 1,737	$ 1,700	$ 1,519	$ 40	$ 42	$ 119	$ 120	$ 986	$ 1,089	$ 1,179	$ 1,228
Net Gains (Losses) Included in Net Income	(2)	(1)	(4)	(1)	(1)	(7)	(8)	(10)		3	1	6							(3)	1	(11)	6	186	(374)	185	(430)	1	1	5	10	(363)	876	(216)	1,207
Net Gains (Losses) Included in Other Comprehensive Income (Loss)	(3)	21	8	37	3	28	17	65	1	3	1	4							1	50	26	103					(2)	(2)		(1)
Purchases											25										25		3	16	5	29							1
Sales				(48)	(20)		(20)												(20)	(7)	(20)	(55)							(7)	(7)	(1)	(2)	(2)	(2)
Principal Payments	(47)	(40)	(81)	(78)	(13)	(31)	(25)	(61)	(1)	(6)	(2)	(15)							(61)	(94)	(108)	(178)					(2)	(4)	(15)	(20)
Issuances																							233	215	487	476
Settlements																															(199)	(603)	(539)	(1,073)
End of Period Balance	547	713	547	713	319	796	319	796	40	112	40	112	9	9	9	9	9	9	915	1,769	915	1,769	2,377	1,594	2,377	1,594	37	37	102	102	423	1,360	423	1,360
Net Change in Unrealized Gains (Losses) Relating to Assets Still Held at End of Period	$ (3)	$ 20	$ 8	$ 33	$ 5	$ 28	$ 18	$ 65	$ 1	$ 3	$ 1	$ 4							$ 3	$ 50	$ 27	$ 101	$ 186	$ (374)	$ 185	$ (430)	$ (1)	$ (2)		$ 1	$ (289)	$ (389)	$ (627)	$ (850)