Acquisition and Discontinued Operations (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012		Mar. 31, 2011		Dec. 31, 2011		Sep. 30, 2011	Dec. 31, 2010
Income (Loss) From Discontinued Operations, Net Of Taxes
Net interest income	$ 553		$ 597
Net interest income (expense) after provision for loan and lease losses	511		637
Noninterest income	472		457
Noninterest expense	703		701
Income taxes	75		111
Income (loss) from discontinued operations, net of taxes	(5)		(11)
Discontinued Assets and Liabilities of our Education Lending Business
Loans, net of unearned income of ($2), ($2) and $1	49,226		48,552		49,575
Less: Allowance for loan and lease losses	944		1,372		1,004
Net loans	48,282		47,180		48,571
Trust accrued income and other assets at fair value	3,091	[1]	3,758	[1]	3,077	[1]
Loans held for sale	511		426		728		479	467
Trust accrued expense and other derivative liabilities at fair value	754		1,106		1,026
Total assets	5,768	[1]	6,393	[1]	5,860	[1]
Total liabilities	2,549	[1]	2,929	[1]	2,550	[1]
Segment, Discontinued Operations [Member]
Income (Loss) From Discontinued Operations, Net Of Taxes
Net interest income	31		36
Provision for loan and lease losses	4		32
Net interest income (expense) after provision for loan and lease losses	27		4
Noninterest income	18		9
Noninterest expense	17		12
Income taxes	(3)		(6)
Income (loss) from discontinued operations, net of taxes	(5)		(11)
Income (loss) before income taxes	(8)		(17)
Discontinued Assets and Liabilities of our Education Lending Business
Loans, net of unearned income of ($2), ($2) and $1	2,927		3,239		3,010
Less: Allowance for loan and lease losses	90		111		104
Net loans	5,625		6,193		5,708
Loans held for sale			14
Total liabilities	2,549		2,929		2,550
Education Lending [Member]
Income (Loss) From Discontinued Operations, Net Of Taxes
Income (loss) from discontinued operations, net of taxes			(11)
Income (loss) before income taxes			(17)
Discontinued Assets and Liabilities of our Education Lending Business
Total assets	5,737		6,360		5,829
Total liabilities	2,542		2,928		2,550
Education Lending [Member] | Segment, Discontinued Operations [Member]
Income (Loss) From Discontinued Operations, Net Of Taxes
Net interest income	31		36
Provision for loan and lease losses	4		32
Net interest income (expense) after provision for loan and lease losses	27		4
Noninterest income	(18)		(10)
Noninterest expense	9		11
Income taxes			(6)
Discontinued Assets and Liabilities of our Education Lending Business
Loans, net of unearned income of ($2), ($2) and $1	2,927		3,239		3,010
Less: Allowance for loan and lease losses	90		111		104
Net loans	5,625		6,193		5,708
Trust accrued income and other assets at fair value	112
Loans held for sale	0		14		0
Trust accrued expense and other derivative liabilities at fair value	30
Trust securities at fair value	2,512
Trust [Member] | Segment, Discontinued Operations [Member]
Discontinued Assets and Liabilities of our Education Lending Business
Trust loans at fair value	2,714		3,065		2,726
Trust accrued income and other assets at fair value	113		153		121
Trust securities at fair value	2,512		2,894		2,522
Trust [Member] | Education Lending [Member] | Segment, Discontinued Operations [Member]
Discontinued Assets and Liabilities of our Education Lending Business
Trust loans at fair value	2,714		3,065		2,726
Trust accrued income and other assets at fair value			153		121
Trust accrued expense and other derivative liabilities at fair value			34		28
Trust securities at fair value	2,512		2,894		2,522
Portfolio [Member] | Segment, Discontinued Operations [Member]
Discontinued Assets and Liabilities of our Education Lending Business
Trust loans at fair value	74				76
Portfolio [Member] | Education Lending [Member] | Segment, Discontinued Operations [Member]
Discontinued Assets and Liabilities of our Education Lending Business
Trust loans at fair value	$ 74				$ 76

[1] The assets of the VIEs can only be used by the particular VIE and there is no recourse to Key with respect to the liabilities of the consolidated LIHTC or education loan securitization trust VIEs.