Acquisitions and Discontinued Operations - Components of Assets and Liabilities of Education Lending Business (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012		Mar. 31, 2012
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loans at fair value	$ 154		$ 157		$ 74
Loans, net of unearned income of ($5), ($5) and ($2)	52,574		52,822		49,226
Less: Allowance for loan and lease losses	893		888		944
Net loans	51,681		51,934		48,282
Accrued income and other assets	2,884	[1]	2,774	[1]	3,070	[1]
Total assets	89,198		89,236		87,431
Trust accrued expense and other liabilities at fair value	1,352		1,387		1,424
Total liabilities	78,819		78,927		77,315
Segment, discontinued operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loans, net of unearned income of ($5), ($5) and ($2)	2,599		2,675		2,927
Less: Allowance for loan and lease losses	49		55		90
Net loans	5,037		5,146		5,625
Accrued income and other assets	97		87		22
Total assets	5,182		5,282		5,790
Total liabilities	2,176		2,220		2,575
Education lending [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total assets	5,116		5,232		5,737
Total liabilities	2,151		2,181		2,542
Education lending [Member] | Segment, discontinued operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loans, net of unearned income of ($5), ($5) and ($2)	2,599		2,675		2,927
Less: Allowance for loan and lease losses	49		55		90
Net loans	5,037		5,146		5,625
Accrued income and other assets	54		60
Trust [Member] | Segment, discontinued operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loans at fair value	2,333		2,369		2,714
Trust accrued income and other assets at fair value	25		26		112
Trust accrued expense and other liabilities at fair value	25		22		30
Trust securities at fair value	2,126		2,159		2,512
Trust [Member] | Education lending [Member] | Segment, discontinued operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loans at fair value	2,333		2,369		2,714
Trust accrued income and other assets at fair value	25		26		112
Trust accrued expense and other liabilities at fair value	25		22		30
Trust securities at fair value	2,126		2,159		2,512
Portfolio [Member] | Segment, discontinued operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loans at fair value	154		157		74
Portfolio [Member] | Education lending [Member] | Segment, discontinued operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loans at fair value	$ 154		$ 157		$ 74

[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.