Line of Business Results (Details 1) (USD $) In Millions, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011		Jun. 30, 2012	Jun. 30, 2011
Supplementary information (Key Corporate Bank lines of business)
Provision (credit) for loan and lease losses	$ 21	$ (8)		$ 63	$ (48)
Noninterest expense	714	680		1,417	1,381
Net income (loss) attributable to Key	236	240		436	503
Real Estate Capital and Corporate Banking Services [Member]
Supplementary information (Key Corporate Bank lines of business)
Total revenue (TE)	176	156		337	324
Provision (credit) for loan and lease losses	5	(49)		4	(39)
Noninterest expense	63	50	[1]	122	118
Net income (loss) attributable to Key	65	97		129	154
Average loans and leases	7,343	7,713		7,521	8,146
Average loans held for sale	337	229		314	185
Average deposits	9,190	7,371		8,705	7,987
Net loan charge-offs	7	26		23	91
Net loan charge-offs to average loans	0.38%	1.35%		0.61%	2.25%
Nonperforming assets at period end	186	245		186	245
Return on average allocated equity	30.90%	31.13%		29.15%	22.72%
Average full-time equivalent employees	950	902		951	892
Equipment Finance [Member]
Supplementary information (Key Corporate Bank lines of business)
Total revenue (TE)	57	63		122	126
Provision (credit) for loan and lease losses	6	(30)		4	(56)
Noninterest expense	37	45		75	98
Net income (loss) attributable to Key	9	30		27	53
Average loans and leases	4,886	4,545		4,833	4,583
Average loans held for sale	23			23	2
Average deposits	7	12		7	9
Net loan charge-offs	4	2		9	12
Net loan charge-offs to average loans	0.33%	0.18%		0.37%	0.53%
Nonperforming assets at period end	33	39		33	39
Return on average allocated equity	14.48%	35.81%		20.88%	31.34%
Average full-time equivalent employees	464	511		466	516
Institutional and Capital Markets [Member]
Supplementary information (Key Corporate Bank lines of business)
Total revenue (TE)	159	172		334	346
Provision (credit) for loan and lease losses	(7)	3		9	(2)
Noninterest expense	118	112		252	219
Net income (loss) attributable to Key	31	37		49	83
Average loans and leases	6,303	4,910		6,204	4,692
Average loans held for sale	154	73		174	102
Average deposits	3,212	2,812		3,270	2,740
Net loan charge-offs	(2)	1		2	1
Net loan charge-offs to average loans	0.13%	0.08%		0.06%	0.04%
Nonperforming assets at period end	$ 29	$ 55		$ 29	$ 55
Return on average allocated equity	17.99%	20.00%		14.10%	22.29%
Average full-time equivalent employees	843	778		839	765

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