Acquisition and Discontinued Operations (Details 7) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012		Dec. 31, 2011		Sep. 30, 2011	Mar. 31, 2011		Dec. 31, 2010
Combined assets and liabilities of the discontinued operations
Cash and due from banks	$ 416		$ 694			$ 540		$ 278
Loans, net of unearned income of ($2), ($2) and $1	49,226		49,575			48,552
Less: Allowance for loan and lease losses	944		1,004			1,372
Net loans	48,282		48,571			47,180
Loans held for sale	511		728		479	426		467
Trust accrued income and other assets at fair value	3,091	[1]	3,077	[1]		3,758	[1]
Total assets	5,768	[1]	5,860	[1]		6,393	[1]
Accrued expense and other liabilities	1,450		1,763			1,931
Total liabilities	2,549	[1]	2,550	[1]		2,929	[1]
Segment, Discontinued Operations [Member]
Combined assets and liabilities of the discontinued operations
Cash and due from banks	30		31			33
Loans, net of unearned income of ($2), ($2) and $1	2,927		3,010			3,239
Less: Allowance for loan and lease losses	90		104			111
Net loans	5,625		5,708			6,193
Loans held for sale						14
Accrued expense and other liabilities	7					1
Total liabilities	2,549		2,550			2,929
Segment, Discontinued Operations [Member] | Trust [Member]
Combined assets and liabilities of the discontinued operations
Trust loans at fair value	2,714		2,726			3,065
Trust accrued income and other assets at fair value	113		121			153
Accrued expense and other liabilities	30		28			34
Trust securities at fair value	2,512		2,522			2,894
Segment, Discontinued Operations [Member] | Portfolio [Member]
Combined assets and liabilities of the discontinued operations
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.