Acquisitions and Discontinued Operations - Components of Assets and Liabilities from Discontinued Operations (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012		Sep. 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	$ 748		$ 584		$ 973		$ 693
Total assets	4,838	[1]	5,282	[1]	5,400	[1]
Total liabilities	2,037	[1]	2,220	[1]	2,368	[1]
Segment, Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash and due from banks	20		23		22
Accrued expense and other liabilities			39		33
Segment, Discontinued Operations [Member] | Victory Capital Management [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash and due from banks			1		1
Accrued income and other assets	31		27		18
Total assets	31		28		19
Accrued expense and other liabilities			38		33
Total liabilities			38		33
Segment, Discontinued Operations [Member] | Austin Capital Management [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash and due from banks	20		22		21
Total assets	20		22		21
Accrued expense and other liabilities			1
Total liabilities			$ 1

[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.