Acquisitions and Discontinued Operations - Combined Assets and Liabilities of Discontinued Operations (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010	Dec. 31, 2009
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash and due from banks	$ 585		$ 694		$ 278	$ 471
Trust loans accounted for at fair value	157
Loans, net of unearned income of ($5) and ($2)	52,822		49,575
Less: Allowance for loan and lease losses	888		1,004
Net loans	51,934		48,571
Accrued income and other assets	2,801	[1]	3,077	[1]
Total assets	89,236		88,785
Trust accrued expense and other liabilities at fair value	1,425		1,763
Total liabilities	78,927		78,863
Segment, discontinued operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash and due from banks	22		31
Loans, net of unearned income of ($5) and ($2)	2,675		3,010
Less: Allowance for loan and lease losses	55		104
Net loans	5,146		5,708
Accrued income and other assets	60		87
Total assets	5,254		5,860
Total liabilities	2,182		2,550
Segment, discontinued operations [Member] | Trust [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Trust loans accounted for at fair value	2,369		2,726
Trust accrued income and other assets at fair value	26		34
Trust accrued expense and other liabilities at fair value	23		28
Trust securities at fair value	2,159		2,522
Segment, discontinued operations [Member] | Portfolio [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Trust loans accounted for at fair value	$ 157		$ 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.