Fair Value Measurement and Fair Value of Financial Instruments - Financial Assets and Financial Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Other assets	$ 2	$ 3
Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Trading account assets	844	1,208
Other assets	3	4
Securities available for sale	23,510	21,352
Trading account liabilities	566	895
Total assets	24,357	22,564
Percentage of Total	100.00%	100.00%
Percentage of Total Company Assets	24.00%	23.00%
Other liabilities	102	95
Total liabilities	668	990
Percentage of Total	100.00%	100.00%
Percentage of Total Company Liabilities	1.00%	1.00%
U.S. Treasury [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Trading account assets	4	1
U.S. government sponsored agencies [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Trading account assets	100	113
Securities available for sale	364	885
State and municipal [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Trading account assets	23	15
Other short-term borrowings [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Trading account assets	20	10
Interest rate derivative contracts [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Trading account assets	626	988
Trading account liabilities	293	602
Commodity derivative contracts [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Trading account assets	6	40
Trading account liabilities	67	98
Foreign exchange derivative contracts [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Trading account assets	40	41
Trading account liabilities	23	65
Equity Derivative contracts [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Trading account assets	25
Trading account liabilities	168	103
U.S. government agency and government sponsored agencies [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Securities available for sale	14,673	13,333
Privately issued [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Securities available for sale	328	443
Commercial mortgage-backed securities [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Securities available for sale	3,750	2,971
CLOs [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Securities available for sale	2,445	1,959
Asset-backed and other [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Securities available for sale	80	146
Direct bank purchase bonds [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Securities available for sale	1,703	1,438
Other [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Securities available for sale	152	158
Equity securities [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Securities available for sale	15	19
Interest rate hedging contracts [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Other assets	1	4
Other liabilities	7
Other derivative contracts [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Other assets	2
Other liabilities	5	3
Securities sold, not yet purchased [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Trading account liabilities	15	27
FDIC clawback liability [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Other liabilities	90	92
Level 1 [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Trading account assets	4	1
Securities available for sale	15	19
Trading account liabilities	4	6
Total assets	19	20
Total liabilities	4	6
Percentage of Total	1.00%	1.00%
Level 1 [Member] | Interest rate derivative contracts [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Trading account assets	3
Trading account liabilities	3	5
Level 1 [Member] | Foreign exchange derivative contracts [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Trading account assets	1	1
Trading account liabilities	1	1
Level 1 [Member] | Equity securities [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Securities available for sale	15	19
Level 2 [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Trading account assets	1,102	1,416
Other assets	1	29
Securities available for sale	21,733	19,834
Trading account liabilities	827	1,202
Total assets	22,836	21,279
Percentage of Total	94.00%	94.00%
Percentage of Total Company Assets	22.00%	22.00%
Other liabilities	8
Total liabilities	835	1,202
Percentage of Total	125.00%	121.00%
Percentage of Total Company Liabilities	1.00%	2.00%
Level 2 [Member] | U.S. Treasury [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Trading account assets	4	1
Level 2 [Member] | U.S. government sponsored agencies [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Trading account assets	100	113
Securities available for sale	364	885
Level 2 [Member] | State and municipal [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Trading account assets	23	15
Level 2 [Member] | Other short-term borrowings [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Trading account assets	20	10
Level 2 [Member] | Interest rate derivative contracts [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Trading account assets	790	1,075
Trading account liabilities	694	1,004
Level 2 [Member] | Commodity derivative contracts [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Trading account assets	106	137
Trading account liabilities	94	110
Level 2 [Member] | Foreign exchange derivative contracts [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Trading account assets	59	65
Trading account liabilities	24	61
Level 2 [Member] | U.S. government agency and government sponsored agencies [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Securities available for sale	14,673	13,333
Level 2 [Member] | Privately issued [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Securities available for sale	328	443
Level 2 [Member] | Commercial mortgage-backed securities [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Securities available for sale	3,750	2,971
Level 2 [Member] | CLOs [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Securities available for sale	2,445	1,959
Level 2 [Member] | Asset-backed and other [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Securities available for sale	80	146
Level 2 [Member] | Other [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Securities available for sale	93	97
Level 2 [Member] | Interest rate hedging contracts [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Other assets	1	28
Other liabilities	7
Level 2 [Member] | Other derivative contracts [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Other assets		1
Other liabilities	1
Level 2 [Member] | Securities sold, not yet purchased [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Trading account liabilities	15	27
Level 3 [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Other assets	2	3
Level 3 [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Trading account assets	182	136
Other assets	2
Securities available for sale	1,762	1,499
Trading account liabilities	183	136
Total assets	1,946	1,635
Percentage of Total	8.00%	7.00%
Percentage of Total Company Assets	2.00%	1.00%
Other liabilities	94	95
Total liabilities	277	231
Percentage of Total	42.00%	23.00%
Level 3 [Member] | Commodity derivative contracts [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Trading account assets	12	30
Trading account liabilities	12	30
Level 3 [Member] | Foreign exchange derivative contracts [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Trading account assets	3	3
Trading account liabilities	3	3
Level 3 [Member] | Equity Derivative contracts [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Trading account assets	167	103
Trading account liabilities	168	103
Level 3 [Member] | Direct bank purchase bonds [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Securities available for sale	1,703	1,438
Level 3 [Member] | Other [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Securities available for sale	59	61
Level 3 [Member] | Other derivative contracts [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Other assets	2
Other liabilities	4	3
Level 3 [Member] | FDIC clawback liability [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Other liabilities	90	92
Netting Adjustment [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Trading account assets	(444)	(345)
Other assets		(25)
Trading account liabilities	(448)	(449)
Total assets	(444)	(370)
Percentage of Total	(2.00%)	(1.00%)
Total liabilities	(448)	(449)
Percentage of Total	(67.00%)	(45.00%)
Percentage of Total Company Liabilities	(1.00%)	(1.00%)
Netting Adjustment [Member] | Interest rate derivative contracts [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Trading account assets	(167)	(87)
Trading account liabilities	(404)	(407)
Netting Adjustment [Member] | Commodity derivative contracts [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Trading account assets	(112)	(127)
Trading account liabilities	(39)	(42)
Netting Adjustment [Member] | Foreign exchange derivative contracts [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Trading account assets	(23)	(28)
Trading account liabilities	(5)
Netting Adjustment [Member] | Equity Derivative contracts [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Trading account assets	(142)	(103)
Netting Adjustment [Member] | Interest rate hedging contracts [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Other assets		(24)
Netting Adjustment [Member] | Other derivative contracts [Member] | Fair Value Measurements Recurring [Member]
Fair Value Inputs, Equity, Quantitative Information [Line Items]
Other assets		$ (1)