Acquisitions and Discontinued Operations - Combined Assets and Liabilities of Discontinued Operations (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012		Jun. 30, 2012		Dec. 31, 2011
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash and due from banks	$ 696		$ 584		$ 716		$ 693
Trust loans accounted for at fair value	151		157		73
Loans, net of unearned income of ($5), ($5), and ($2)	53,101		52,822		49,605
Less: Allowance for loan and lease losses	876		888		888
Net loans	52,225		51,934		48,717
Accrued income and other assets	2,864	[1]	2,774	[1]	2,967	[1]
Total assets	90,639		89,236		86,523
Trust accrued expense and other liabilities at fair value	1,421		1,387		1,390
Total liabilities	80,378		78,927		76,347
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		23		23
Loans, net of unearned income of ($5), ($5), and ($2)	2,524		2,675		2,830
Less: Allowance for loan and lease losses	41		55		79
Net loans	4,951		5,146		5,404
Accrued income and other assets	87		87		87
Total assets	5,084		5,282		5,545
Accrued expense and other liabilities	30		39		27
Total liabilities	2,169		2,220		2,428
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	2,317		2,369		2,580
Trust accrued income and other assets at fair value	24		26		31
Trust accrued expense and other liabilities at fair value	21		22		28
Trust securities at fair value	2,118		2,159		2,373
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	$ 151		$ 157		$ 73

[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.