Condensed Financial Information of the Parent Company - Condensed Statements of Income (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Condensed Financial Statements, Captions [Line Items]
Other income	$ 44	[1]	$ 59	[1]	$ 105	[1]
Total interest income	2,554		2,620		2,705
Interest on long-term debt with subsidiary trusts	133		127		173
Income (loss) before income taxes and equity in net income (loss) less dividends from subsidiaries	1,272		1,141		1,073
Income tax (expense) benefit	(326)		(271)		(231)
NET INCOME (LOSS)	907		910		865
Less: Net income attributable to noncontrolling interests	7				7
NET INCOME (LOSS) ATTRIBUTABLE TO KEY	900		910		858
Key [Member]
Condensed Financial Statements, Captions [Line Items]
Interest income from subsidiaries	16		26		36
Other income	15		15		66
Total interest income	331		641		1,877
Interest on long-term debt with subsidiary trusts	10		14		29
Interest on other borrowed funds	53		59		86
Personnel and other expense	40		65		68
Total expense	103		138		183
Income (loss) before income taxes and equity in net income (loss) less dividends from subsidiaries	228		503		1,694
Income tax (expense) benefit	45		33		48
Income (loss) before equity in net income (loss) less dividends from subsidiaries	273		536		1,742
Equity in net income (loss) less dividends from subsidiaries	634		374		(877)
NET INCOME (LOSS)	907		910		865
Less: Net income attributable to noncontrolling interests	7				7
NET INCOME (LOSS) ATTRIBUTABLE TO KEY	900		910		858
Key [Member] | Banks [Member]
Condensed Financial Statements, Captions [Line Items]
Bank subsidiaries	$ 300		$ 600		$ 1,775

[1] For the years ended December 31, 2014, 2013, and 2012, net securities gains (losses) totaled less than $1 million, $1 million, and less than $1 million, respectively. For 2014, 2013, and 2012, we did not have any impairment losses related to securities.