Fair Value Measurement and Fair Value of Financial Instruments (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Assets
Securities available for sale	$ 20,545	$ 22,833
Fair Value Measurements Recurring [Member]
Assets
Trading account assets	1,237	1,135
Securities available for sale	20,545	22,833
Other assets	5
Total assets	21,787	23,968
Percentage of Total	100.00%	100.00%
Percentage of Total Company Assets	25.00%	27.00%
Liabilities
Trading account liabilities	976	1,040
Other liabilities	72	61
Total liabilities	1,048	1,101
Percentage of Total	100.00%	100.00%
Percentage of Total Company Liabilities	1.00%	1.00%
Level1 [Member] \| Fair Value Measurements Recurring [Member]
Assets
Trading account assets	2	33
Securities available for sale	86	7,077
Total assets	88	7,110
Percentage of Total		30.00%
Percentage of Total Company Assets		8.00%
Liabilities
Trading account liabilities	7	25
Total liabilities	7	25
Percentage of Total	1.00%	2.00%
Level2 [Member] \| Fair Value Measurements Recurring [Member]
Assets
Trading account assets	1,532	1,392
Securities available for sale	19,325	15,708
Other assets	25	3
Total assets	20,882	17,103
Percentage of Total	96.00%	71.00%
Percentage of Total Company Assets	24.00%	19.00%
Liabilities
Trading account liabilities	1,258	1,293
Other liabilities		10
Total liabilities	1,258	1,303
Percentage of Total	120.00%	119.00%
Percentage of Total Company Liabilities	2.00%	1.00%
Level3 [Member] \| Fair Value Measurements Recurring [Member]
Assets
Trading account assets	118
Securities available for sale	1,134	48
Total assets	1,252	48
Percentage of Total	6.00%
Percentage of Total Company Assets	1.00%
Liabilities
Trading account liabilities	118
Other liabilities	72	51
Total liabilities	190	51
Percentage of Total	18.00%	5.00%
Netting Adjustment [Member] \| Fair Value Measurements Recurring [Member]
Assets
Trading account assets	(415)	(290)
Other assets	(20)	(3)
Total assets	(435)	(293)
Percentage of Total	(2.00%)	1.00%
Liabilities
Trading account liabilities	(407)	(278)
Total liabilities	(407)	(278)
Percentage of Total	39.00%	25.00%
Percentage of Total Company Liabilities	(1.00%)
U. S. Treasury [Member] \| Fair Value Measurements Recurring [Member]
Assets
Trading account assets	63	14
U. S. Treasury [Member] \| Level1 [Member] \| Fair Value Measurements Recurring [Member]
Assets
Trading account assets		14
U. S. Treasury [Member] \| Level2 [Member] \| Fair Value Measurements Recurring [Member]
Assets
Trading account assets	63
U.S. government sponsored agencies [Member]
Assets
Securities available for sale	5,459	6,997
U.S. government sponsored agencies [Member] \| Fair Value Measurements Recurring [Member]
Assets
Trading account assets	78	17
Securities available for sale	5,459	6,997
U.S. government sponsored agencies [Member] \| Level1 [Member] \| Fair Value Measurements Recurring [Member]
Assets
Trading account assets		17
Securities available for sale		6,997
U.S. government sponsored agencies [Member] \| Level2 [Member] \| Fair Value Measurements Recurring [Member]
Assets
Trading account assets	78
Securities available for sale	5,459	13,485
State and municipal [Member] \| Fair Value Measurements Recurring [Member]
Assets
Trading account assets	60	17
State and municipal [Member] \| Level2 [Member] \| Fair Value Measurements Recurring [Member]
Assets
Trading account assets	60	17
Commercial paper [Member] \| Fair Value Measurements Recurring [Member]
Assets
Trading account assets	10	30
Commercial paper [Member] \| Level2 [Member] \| Fair Value Measurements Recurring [Member]
Assets
Trading account assets	10	30
Interest rate contracts [Member] \| Fair Value Measurements Recurring [Member]
Assets
Trading account assets	908	837
Other assets	5
Liabilities
Trading account liabilities	569	641
Interest rate contracts [Member] \| Level1 [Member] \| Fair Value Measurements Recurring [Member]
Assets
Trading account assets		1
Liabilities
Trading account liabilities	5	4
Interest rate contracts [Member] \| Level2 [Member] \| Fair Value Measurements Recurring [Member]
Assets
Trading account assets	997	921
Other assets	25	3
Liabilities
Trading account liabilities	935	865
Interest rate contracts [Member] \| Netting Adjustment [Member] \| Fair Value Measurements Recurring [Member]
Assets
Trading account assets	(89)	(85)
Other assets	(20)	(3)
Liabilities
Trading account liabilities	(371)	(228)
Commodity contracts [Member] \| Fair Value Measurements Recurring [Member]
Assets
Trading account assets	49	85
Liabilities
Trading account liabilities	181	204
Commodity contracts [Member] \| Level2 [Member] \| Fair Value Measurements Recurring [Member]
Assets
Trading account assets	224	250
Liabilities
Trading account liabilities	187	247
Commodity contracts [Member] \| Level3 [Member] \| Fair Value Measurements Recurring [Member]
Assets
Trading account assets	25
Liabilities
Trading account liabilities	25
Commodity contracts [Member] \| Netting Adjustment [Member] \| Fair Value Measurements Recurring [Member]
Assets
Trading account assets	(200)	(165)
Liabilities
Trading account liabilities	(31)	(43)
Foreign exchange contracts [Member] \| Fair Value Measurements Recurring [Member]
Assets
Trading account assets	67	48
Liabilities
Trading account liabilities	100	88
Foreign exchange contracts [Member] \| Level1 [Member] \| Fair Value Measurements Recurring [Member]
Assets
Trading account assets	2	1
Liabilities
Trading account liabilities	2	1
Foreign exchange contracts [Member] \| Level2 [Member] \| Fair Value Measurements Recurring [Member]
Assets
Trading account assets	97	87
Liabilities
Trading account liabilities	99	94
Foreign exchange contracts [Member] \| Level3 [Member] \| Fair Value Measurements Recurring [Member]
Assets
Trading account assets	4
Liabilities
Trading account liabilities	4
Foreign exchange contracts [Member] \| Netting Adjustment [Member] \| Fair Value Measurements Recurring [Member]
Assets
Trading account assets	(36)	(40)
Liabilities
Trading account liabilities	(5)	(7)
Equity contracts [Member] \| Fair Value Measurements Recurring [Member]
Assets
Trading account assets	2	87
Liabilities
Trading account liabilities	89	87
Equity contracts [Member] \| Level2 [Member] \| Fair Value Measurements Recurring [Member]
Assets
Trading account assets		87
Liabilities
Trading account liabilities		87
Equity contracts [Member] \| Level3 [Member] \| Fair Value Measurements Recurring [Member]
Assets
Trading account assets	89
Liabilities
Trading account liabilities	89
Equity contracts [Member] \| Netting Adjustment [Member] \| Fair Value Measurements Recurring [Member]
Assets
Trading account assets	(87)
Credit Contracts [Member] \| Level2 [Member] \| Fair Value Measurements Recurring [Member]
Assets
Trading account assets	3
Credit Contracts [Member] \| Netting Adjustment [Member] \| Fair Value Measurements Recurring [Member]
Assets
Trading account assets	(3)
Securities sold, not yet purchased [Member] \| Fair Value Measurements Recurring [Member]
Liabilities
Trading account liabilities	37	20
Securities sold, not yet purchased [Member] \| Level1 [Member] \| Fair Value Measurements Recurring [Member]
Liabilities
Trading account liabilities		20
Securities sold, not yet purchased [Member] \| Level2 [Member] \| Fair Value Measurements Recurring [Member]
Liabilities
Trading account liabilities	37
U.S. government and government sponsored agencies [Member]
Assets
Securities available for sale	11,337	13,485
U.S. government and government sponsored agencies [Member] \| Fair Value Measurements Recurring [Member]
Assets
Securities available for sale	11,337	13,485
U.S. government and government sponsored agencies [Member] \| Level2 [Member] \| Fair Value Measurements Recurring [Member]
Assets
Securities available for sale	11,337
Privately issued [Member] \| Fair Value Measurements Recurring [Member]
Assets
Securities available for sale	623	738
Privately issued [Member] \| Level2 [Member] \| Fair Value Measurements Recurring [Member]
Assets
Securities available for sale	623	738
Commercial mortgage-backed securities [Member]
Assets
Securities available for sale	1,554	1,060
Commercial mortgage-backed securities [Member] \| Fair Value Measurements Recurring [Member]
Assets
Securities available for sale	1,554	1,060
Commercial mortgage-backed securities [Member] \| Level2 [Member] \| Fair Value Measurements Recurring [Member]
Assets
Securities available for sale	1,554	1,060
Other debt securities [Member]
Assets
Securities available for sale	1,486	472
Other debt securities [Member] \| Fair Value Measurements Recurring [Member]
Assets
Securities available for sale	1,486	472
Other debt securities [Member] \| Level2 [Member] \| Fair Value Measurements Recurring [Member]
Assets
Securities available for sale	352	425
Other debt securities [Member] \| Level3 [Member] \| Fair Value Measurements Recurring [Member]
Assets
Securities available for sale	1,134	47
Equity securities [Member]
Assets
Securities available for sale	86	81
Equity securities [Member] \| Fair Value Measurements Recurring [Member]
Assets
Securities available for sale	86	81
Equity securities [Member] \| Level1 [Member] \| Fair Value Measurements Recurring [Member]
Assets
Securities available for sale	86	80
Equity securities [Member] \| Level3 [Member] \| Fair Value Measurements Recurring [Member]
Assets
Securities available for sale		$ 1

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