Restrictions on Cash, Dividends and Lending Activities - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014
Restricted Cash and Cash Equivalents Items [Line Items]
Average reserve balance maintained	$ 181,000,000
Short-term investments held for discharge of obligations	2,200,000,000
Capital infusions to subsidiary	0
Capital infusions to nonbank subsidiaries	9,000,000
KeyBank (consolidated) [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Capacity to pay dividends	935,000,000
Dividends paid by non banking subsidiaries	$ 300,000,000