Fair Value Measurements - Change in Fair Values of Level 3 Financial Instruments (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended		3 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 Interest Rate [Member]	Jun. 30, 2012 Interest Rate [Member]	Jun. 30, 2013 Interest Rate [Member]	Jun. 30, 2012 Interest Rate [Member]	Jun. 30, 2013 Energy and Commodity [Member]	Dec. 31, 2012 Energy and Commodity [Member]	Jun. 30, 2012 Energy and Commodity [Member]	Mar. 31, 2012 Energy and Commodity [Member]	Dec. 31, 2011 Energy and Commodity [Member]	Jun. 30, 2013 Credit [Member]	Jun. 30, 2012 Credit [Member]	Jun. 30, 2013 Credit [Member]	Jun. 30, 2012 Credit [Member]	Jun. 30, 2013 Trading Account Assets [Member] Other Mortgage-Backed Securities [Member]	Jun. 30, 2012 Trading Account Assets [Member] Other Mortgage-Backed Securities [Member]	Mar. 31, 2012 Trading Account Assets [Member] Other Mortgage-Backed Securities [Member]	Jun. 30, 2013 Trading Account Assets [Member] State and Political Subdivisions [Member]	Jun. 30, 2012 Trading Account Assets [Member] State and Political Subdivisions [Member]	Jun. 30, 2013 Trading Account Assets [Member] State and Political Subdivisions [Member]	Jun. 30, 2012 Trading Account Assets [Member] State and Political Subdivisions [Member]	Jun. 30, 2013 Trading Account Assets [Member] Other Securities [Member]	Jun. 30, 2013 Trading Account Assets [Member] Other Securities [Member]	Jun. 30, 2013 Other Investments [Member] Principal Investments Direct [Member]	Jun. 30, 2012 Other Investments [Member] Principal Investments Direct [Member]	Jun. 30, 2013 Other Investments [Member] Principal Investments Direct [Member]	Jun. 30, 2012 Other Investments [Member] Principal Investments Direct [Member]	Jun. 30, 2013 Other Investments [Member] Principal Investments Indirect [Member]	Jun. 30, 2012 Other Investments [Member] Principal Investments Indirect [Member]	Jun. 30, 2013 Other Investments [Member] Principal Investments Indirect [Member]	Jun. 30, 2012 Other Investments [Member] Principal Investments Indirect [Member]	Jun. 30, 2012 Other Investments [Member] Equity and Mezzanine Investments Direct [Member]	Jun. 30, 2013 Other Investments [Member] Equity and Mezzanine Investments Direct [Member]	Jun. 30, 2012 Other Investments [Member] Equity and Mezzanine Investments Direct [Member]	Jun. 30, 2013 Other Investments [Member] Equity and Mezzanine Investments Indirect [Member]	Jun. 30, 2012 Other Investments [Member] Equity and Mezzanine Investments Indirect [Member]	Jun. 30, 2013 Other Investments [Member] Equity and Mezzanine Investments Indirect [Member]	Jun. 30, 2012 Other Investments [Member] Equity and Mezzanine Investments Indirect [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 27	$ 36	$ 19	$ 38	$ 4	$ 1	$ (1)	$ (1)	$ (1)	$ 4	$ 5	$ 4	$ (21)		$ 35	$ 1	$ 3		$ 3				$ 191	$ 226	$ 191	$ 225	$ 435	$ 485	$ 436	$ 473	$ 15		$ 15	$ 39	$ 42	$ 41	$ 36
Gains (losses) included in earnings		2	(3)	(3)	(3)					(2)	(2)	(3)	(7)	4	2			(5)		(2)	2	3	(1)	7	(5)	8	7	20	19	43	3		3	2	5	2	6
Purchases				1																				9	4	10	5	10	11	20					1		4
Sales			(1)	(1)										(4)	(32)		(3)		(3)				(4)	(11)	(4)	(12)	(21)	(33)	(40)	(54)
Settlements										2	2	3	33					5		2	(2)	(3)												(9)	(2)	(11)	(3)
Transfers into Level 3	25		39	4														57		57															(3)
Transfers out of Level 3	(27)	(3)	(29)	(4)											(4)
Ending Balance	25	35	25	35	1	1	(1)	(1)	(1)	4	5	4	5		1	1		57		57			186	231	186	231	426	482	426	482	18		18	32	43	32	43
Unrealized Gains (Losses) Included In Earnings																		$ (5)		$ (2)		$ 1	$ (7)	$ 7	$ (11)	$ 8		$ 9	$ 4	$ 28	$ 4	$ 3	$ 10	$ 2	$ 2	$ 2	$ 6