Line of Business Results (Details 1) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Supplementary information (Key Community Banking lines of business)
Provision (credit) for loan and lease losses	$ (60)	$ 638	$ 3,159
Noninterest expense	2,790	3,034	3,554
Net income (loss) attributable to Key	920	554	(1,335)
Regional Banking [Member]
Supplementary information (Key Community Banking lines of business)
Total revenue (TE)	1,774	1,923	2,055
Provision (credit) for loan and lease losses	183	355	467
Noninterest expense	1,633	1,644	1,709
Net income (loss) attributable to Key	30	7	(26)
Average loans and leases	17,464	18,256	19,540
Average loans held for sale	59	79	146
Average deposits	41,578	44,261	48,139
Net loan charge-offs	239	346	285
Net loan charge-offs to average loans	1.37%	1.90%	1.46%
Nonperforming assets at year end	287	326	319
Return on average allocated equity	1.35%	0.30%	(1.16%)
Average full-time equivalent employees	8,171	7,900	8,217
Commercial Banking [Member]
Supplementary information (Key Community Banking lines of business)
Total revenue (TE)	460	467	425
Provision (credit) for loan and lease losses	(23)	58	264
Noninterest expense	192	174	228
Net income (loss) attributable to Key	183	148	(42)
Average loans and leases	8,844	8,788	10,207
Average loans held for sale	17	12	1
Average deposits	6,315	5,391	4,386
Net loan charge-offs	47	163	170
Net loan charge-offs to average loans	0.53%	1.85%	1.67%
Nonperforming assets at year end	$ 128	$ 171	$ 225
Return on average allocated equity	19.28%	12.63%	(3.28%)
Average full-time equivalent employees	369	355	361