Line of Business Results (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
SUMMARY OF OPERATIONS
Net interest income (TE)	$ 2,267	$ 2,511	$ 2,380
Noninterest income	1,808	1,954	2,035
Provision (credit) for loan and lease losses	(60)	638	3,159
Other noninterest expense	157	203	204
Income (loss) from continuing operations before income taxes (TE)	1,345	793	(2,298)
Allocated income taxes and TE adjustments	369	186	(1,035)
Income (loss) from continuing operations	976	607	(1,263)
Income (loss) from discontinued operations, net of taxes	(44)	(23)	(48)
NET INCOME (LOSS)	932	584	(1,311)
Less: Net income (loss) attributable to noncontrolling interests	12	30	24
NET INCOME (LOSS) ATTRIBUTABLE TO KEY	920	554	(1,335)
OTHER FINANCIAL DATA
Expenditures for additions to long-lived assets	103	100	96
Line of Business Results (Textual) [Abstract]
Federal income tax rate	35.00%	35.00%	35.00%
State income tax rate	2.20%
Percentage of debt service provided by rental income from nonaffiliated third parties	50.00%
Key [Member]
SUMMARY OF OPERATIONS
Net interest income (TE)	2,292	2,537	2,406
Noninterest income	1,808	1,954	2,035
Total revenue (TE)	4,100	4,491	4,441
Provision (credit) for loan and lease losses	(60)	638	3,159
Depreciation and amortization expense	270	330	389
Other noninterest expense	2,520	2,704	3,165
Income (loss) from continuing operations before income taxes (TE)	1,370	819	(2,272)
Allocated income taxes and TE adjustments	394	212	(1,009)
Income (loss) from continuing operations	976	607	(1,263)
Income (loss) from discontinued operations, net of taxes	(44)	(23)	(48)
NET INCOME (LOSS)	932	584	(1,311)
Less: Net income (loss) attributable to noncontrolling interests	12	30	24
NET INCOME (LOSS) ATTRIBUTABLE TO KEY	920	554	(1,335)
AVERAGE BALANCES
Loans and leases	48,606	53,971	66,386
Total assets	82,093	87,474	95,171
Deposits	59,263	63,392	67,045
OTHER FINANCIAL DATA
Expenditures for additions to long-lived assets	211	176	275
Net loan charge-offs	541	1,570	2,257
Return on average allocated equity	9.51%	5.30%	(12.15%)
Return on average allocated equity, Total	9.08%	5.08%	(12.60%)
Average full-time equivalent employees	15,381	15,610	16,698
Key Community Bank [Member]
SUMMARY OF OPERATIONS
Net interest income (TE)	1,488	1,618	1,722
Noninterest income	746	772	758
Total revenue (TE)	2,234	2,390	2,480
Provision (credit) for loan and lease losses	160	413	731
Depreciation and amortization expense	38	37	42
Other noninterest expense	1,787	1,781	1,895
Income (loss) from continuing operations before income taxes (TE)	249	159	(188)
Allocated income taxes and TE adjustments	36	4	(120)
Income (loss) from continuing operations	213	155	(68)
NET INCOME (LOSS)	213	155	(68)
NET INCOME (LOSS) ATTRIBUTABLE TO KEY	213	155	(68)
AVERAGE BALANCES
Loans and leases	26,308	27,044	29,747
Total assets	29,744	30,254	32,564
Deposits	47,893	49,652	52,525
OTHER FINANCIAL DATA
Expenditures for additions to long-lived assets	118	110	139
Net loan charge-offs	286	509	455
Return on average allocated equity	6.73%	4.45%	(1.93%)
Return on average allocated equity, Total	6.73%	4.45%	(1.93%)
Average full-time equivalent employees	8,540	8,255	8,578
Key Corporate Banking [Member]
SUMMARY OF OPERATIONS
Net interest income (TE)	703	796	870
Noninterest income	866	839	693
Total revenue (TE)	1,569	1,635	1,563
Provision (credit) for loan and lease losses	(198)	(28)	1,826
Depreciation and amortization expense	71	94	117
Other noninterest expense	806	904	1,132
Income (loss) from continuing operations before income taxes (TE)	890	665	(1,512)
Allocated income taxes and TE adjustments	325	242	(520)
Income (loss) from continuing operations	565	423	(992)
NET INCOME (LOSS)	565	423	(992)
Less: Net income (loss) attributable to noncontrolling interests		(1)	(5)
NET INCOME (LOSS) ATTRIBUTABLE TO KEY	565	424	(987)
AVERAGE BALANCES
Loans and leases	17,402	20,370	27,235
Total assets	21,547	24,348	32,965
Deposits	10,795	12,235	12,709
OTHER FINANCIAL DATA
Expenditures for additions to long-lived assets	15		9
Net loan charge-offs	138	607	1,260
Return on average allocated equity	25.07%	13.65%	(26.19%)
Return on average allocated equity, Total	25.07%	13.65%	(26.19%)
Average full-time equivalent employees	2,231	2,192	2,353
Other Segments [Member]
SUMMARY OF OPERATIONS
Net interest income (TE)	83	98	(175)
Noninterest income	234	327	473
Total revenue (TE)	317	425	298
Provision (credit) for loan and lease losses	(17)	261	592
Depreciation and amortization expense	18	38	69
Other noninterest expense	80	157	294
Income (loss) from continuing operations before income taxes (TE)	236	(31)	(657)
Allocated income taxes and TE adjustments	43	(62)	(268)
Income (loss) from continuing operations	193	31	(389)
NET INCOME (LOSS)	193	31	(389)
Less: Net income (loss) attributable to noncontrolling interests	12	31	29
NET INCOME (LOSS) ATTRIBUTABLE TO KEY	181		(418)
AVERAGE BALANCES
Loans and leases	4,837	6,507	9,357
Total assets	29,666	30,816	28,676
Deposits	725	1,597	2,427
OTHER FINANCIAL DATA
Net loan charge-offs	117	454	543
Return on average allocated equity	24.01%		(31.69%)
Return on average allocated equity, Total	0.00%		(31.69%)
Average full-time equivalent employees	24	187	232
Total Segments [Member]
SUMMARY OF OPERATIONS
Net interest income (TE)	2,274	2,512	2,417
Noninterest income	1,846	1,938	1,924
Total revenue (TE)	4,120	4,450	4,341
Provision (credit) for loan and lease losses	(55)	646	3,149
Depreciation and amortization expense	127	169	228
Other noninterest expense	2,673	2,842	3,321
Income (loss) from continuing operations before income taxes (TE)	1,375	793	(2,357)
Allocated income taxes and TE adjustments	404	184	(908)
Income (loss) from continuing operations	971	609	(1,449)
NET INCOME (LOSS)	971	609	(1,449)
Less: Net income (loss) attributable to noncontrolling interests	12	30	24
NET INCOME (LOSS) ATTRIBUTABLE TO KEY	959	579	(1,473)
AVERAGE BALANCES
Loans and leases	48,547	53,921	66,339
Total assets	80,957	85,418	94,205
Deposits	59,413	63,484	67,661
OTHER FINANCIAL DATA
Expenditures for additions to long-lived assets	133	110	148
Net loan charge-offs	541	1,570	2,258
Return on average allocated equity	15.54%	7.59%	(17.10%)
Return on average allocated equity, Total	15.54%	7.59%	(17.10%)
Average full-time equivalent employees	10,795	10,634	11,163
Reconciling Items [Member]
SUMMARY OF OPERATIONS
Net interest income (TE)	18	25	(11)
Noninterest income	(38)	16	111
Total revenue (TE)	(20)	41	100
Provision (credit) for loan and lease losses	(5)	(8)	10
Depreciation and amortization expense	143	161	161
Other noninterest expense	(153)	(138)	(156)
Income (loss) from continuing operations before income taxes (TE)	(5)	26	85
Allocated income taxes and TE adjustments	(10)	28	(101)
Income (loss) from continuing operations	5	(2)	186
Income (loss) from discontinued operations, net of taxes	(44)	(23)	(48)
NET INCOME (LOSS)	(39)	(25)	138
NET INCOME (LOSS) ATTRIBUTABLE TO KEY	(39)	(25)	138
AVERAGE BALANCES
Loans and leases	59	50	47
Total assets	1,136	2,056	966
Deposits	(150)	(92)	(616)
OTHER FINANCIAL DATA
Expenditures for additions to long-lived assets	78	66	127
Net loan charge-offs			(1)
Return on average allocated equity	0.13%	(0.06%)	9.39%
Return on average allocated equity, Total	(0.98%)	(0.77%)	6.97%
Average full-time equivalent employees	4,586	4,976	5,535
Line of Business Results (Textual) [Abstract]
Gain from sales of claims			32
Gain from sales of claims, net of tax			20
Reconciling Items [Member] | Internal Revenue Service (IRS) [Member]
Line of Business Results (Textual) [Abstract]
Credit to income taxes			106
Visa Inc [Member]
Line of Business Results (Textual) [Abstract]
Gain from sale of equity interest in visa Inc.			105
Gain from sale of equity interest in visa Inc. net of tax			$ 65