Line of Business Results (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
SUMMARY OF OPERATIONS
Net interest income (TE)	$ 538	$ 564	$ 1,091	$ 1,161
Noninterest income	485	454	957	911
Provision (credit) for loan and lease losses	21	(8)	63	(48)
Other noninterest expense	48	41	81	58
Income (loss) from continuing operations before income taxes (TE)	288	346	568	739
Allocated income taxes and TE adjustments	57	94	132	205
Income (loss) from continuing operations	231	252	436	534
Income (loss) from discontinued operations, net of taxes	10	(9)	5	(20)
NET INCOME (LOSS)	241	243	441	514
Less: Net income (loss) attributable to noncontrolling interests	5	3	5	11
NET INCOME (LOSS) ATTRIBUTABLE TO KEY	236	240	436	503
Key [Member]
SUMMARY OF OPERATIONS
Net interest income (TE)	544	570	1,103	1,174
Noninterest income	485	454	957	911
Total revenue (TE)	1,029	1,024	2,060	2,085
Provision (credit) for loan and lease losses	21	(8)	63	(48)
Depreciation and amortization expense	59	69	119	143
Other noninterest expense	655	611	1,298	1,238
Income (loss) from continuing operations before income taxes (TE)	294	352	580	752
Allocated income taxes and TE adjustments	63	100	144	218
Income (loss) from continuing operations	231	252	436	534
Income (loss) from discontinued operations, net of taxes	10	(9)	5	(20)
NET INCOME (LOSS)	241	243	441	514
Less: Net income (loss) attributable to noncontrolling interests	5	3	5	11
NET INCOME (LOSS) ATTRIBUTABLE TO KEY	236	240	436	503
AVERAGE BALANCES
Loans and leases	49,446	48,454	49,438	48,881
Total assets	80,920	81,386	80,693	82,832
Deposits	61,063	58,541	60,347	59,286
OTHER FINANCIAL DATA
Net loan charge-offs	77	134	178	327
Return on average allocated equity	9.00%	10.45%	8.63%	10.16%
Return on average allocated equity, Total	9.40%	10.07%	8.73%	9.77%
Average full-time equivalent employees	15,455	15,349	15,430	15,326
Community Bank [Member]
SUMMARY OF OPERATIONS
Net interest income (TE)	348	374	701	752
Noninterest income	189	185	365	371
Total revenue (TE)	537	559	1,066	1,123
Provision (credit) for loan and lease losses	11	79	13	90
Depreciation and amortization expense	9	10	19	19
Other noninterest expense	467	437	914	874
Income (loss) from continuing operations before income taxes (TE)	50	33	120	140
Allocated income taxes and TE adjustments	9	(1)	21	25
Income (loss) from continuing operations	41	34	99	115
Income (loss) from discontinued operations, net of taxes
NET INCOME (LOSS)	41	34	99	115
Less: Net income (loss) attributable to noncontrolling interests
NET INCOME (LOSS) ATTRIBUTABLE TO KEY	41	34	99	115
AVERAGE BALANCES
Loans and leases	27,043	26,242	26,830	26,277
Total assets	30,638	29,687	30,416	29,713
Deposits	48,253	47,719	48,011	47,912
OTHER FINANCIAL DATA
Net loan charge-offs	50	79	99	155
Return on average allocated equity	5.73%	4.22%	6.82%	7.11%
Return on average allocated equity, Total	5.73%	4.22%	6.82%	7.11%
Average full-time equivalent employees	8,757	8,504	8,738	8,441
Key Corporate Bank [Member]
SUMMARY OF OPERATIONS
Net interest income (TE)	182	176	369	362
Noninterest income	210	215	424	434
Total revenue (TE)	392	391	793	796
Provision (credit) for loan and lease losses	4	(76)	17	(97)
Depreciation and amortization expense	13	19	26	39
Other noninterest expense	205	188	423	396
Income (loss) from continuing operations before income taxes (TE)	170	260	327	458
Allocated income taxes and TE adjustments	62	95	119	168
Income (loss) from continuing operations	108	165	208	290
Income (loss) from discontinued operations, net of taxes
NET INCOME (LOSS)	108	165	208	290
Less: Net income (loss) attributable to noncontrolling interests	3	1	3
NET INCOME (LOSS) ATTRIBUTABLE TO KEY	105	164	205	290
AVERAGE BALANCES
Loans and leases	18,532	17,168	18,558	17,421
Total assets	22,715	21,468	22,789	21,607
Deposits	12,409	10,195	11,982	10,736
OTHER FINANCIAL DATA
Net loan charge-offs	9	29	34	104
Return on average allocated equity	23.61%	28.26%	22.30%	23.78%
Return on average allocated equity, Total	23.61%	28.26%	22.30%	23.78%
Average full-time equivalent employees	2,257	2,191	2,256	2,173
Other Segments [Member]
SUMMARY OF OPERATIONS
Net interest income (TE)	12	13	27	46
Noninterest income	87	55	176	115
Total revenue (TE)	99	68	203	161
Provision (credit) for loan and lease losses	6	(10)	33	(35)
Depreciation and amortization expense	2	5	5	10
Other noninterest expense	19	20	40	44
Income (loss) from continuing operations before income taxes (TE)	72	53	125	142
Allocated income taxes and TE adjustments	16	9	24	32
Income (loss) from continuing operations	56	44	101	110
Income (loss) from discontinued operations, net of taxes
NET INCOME (LOSS)	56	44	101	110
Less: Net income (loss) attributable to noncontrolling interests	2	2	2	11
NET INCOME (LOSS) ATTRIBUTABLE TO KEY	54	42	99	99
AVERAGE BALANCES
Loans and leases	3,804	4,985	3,997	5,139
Total assets	26,862	28,965	26,723	30,157
Deposits	510	801	498	786
OTHER FINANCIAL DATA
Net loan charge-offs	18	26	45	69
Return on average allocated equity	31.57%	20.82%	28.73%	24.29%
Return on average allocated equity, Total	31.57%	20.82%	28.73%	24.29%
Average full-time equivalent employees	6	23	5	43
Total Segments [Member]
SUMMARY OF OPERATIONS
Net interest income (TE)	542	563	1,097	1,160
Noninterest income	486	455	965	920
Total revenue (TE)	1,028	1,018	2,062	2,080
Provision (credit) for loan and lease losses	21	(7)	63	(42)
Depreciation and amortization expense	24	34	50	68
Other noninterest expense	691	645	1,377	1,314
Income (loss) from continuing operations before income taxes (TE)	292	346	572	740
Allocated income taxes and TE adjustments	87	103	164	225
Income (loss) from continuing operations	205	243	408	515
Income (loss) from discontinued operations, net of taxes
NET INCOME (LOSS)	205	243	408	515
Less: Net income (loss) attributable to noncontrolling interests	5	3	5	11
NET INCOME (LOSS) ATTRIBUTABLE TO KEY	200	240	403	504
AVERAGE BALANCES
Loans and leases	49,379	48,395	49,385	48,837
Total assets	80,215	80,120	79,928	81,477
Deposits	61,172	58,715	60,491	59,434
OTHER FINANCIAL DATA
Net loan charge-offs	77	134	178	328
Return on average allocated equity	15.02%	15.12%	14.83%	15.54%
Return on average allocated equity, Total	15.02%	15.12%	14.83%	15.54%
Average full-time equivalent employees	11,020	10,718	10,999	10,657
Reconciling Items [Member]
SUMMARY OF OPERATIONS
Net interest income (TE)	2	7	6	14
Noninterest income	(1)	(1)	(8)	(9)
Total revenue (TE)	1	6	(2)	5
Provision (credit) for loan and lease losses		(1)		(6)
Depreciation and amortization expense	35	35	69	75
Other noninterest expense	(36)	(34)	(79)	(76)
Income (loss) from continuing operations before income taxes (TE)	2	6	8	12
Allocated income taxes and TE adjustments	(24)	(3)	(20)	(7)
Income (loss) from continuing operations	26	9	28	19
Income (loss) from discontinued operations, net of taxes	10	(9)	5	(20)
NET INCOME (LOSS)	36		33	(1)
Less: Net income (loss) attributable to noncontrolling interests
NET INCOME (LOSS) ATTRIBUTABLE TO KEY	36		33	(1)
AVERAGE BALANCES
Loans and leases	67	59	53	44
Total assets	705	1,266	765	1,355
Deposits	(109)	(174)	(144)	(148)
OTHER FINANCIAL DATA
Net loan charge-offs				$ (1)
Return on average allocated equity	2.20%	1.13%	1.23%	1.00%
Return on average allocated equity, Total	3.05%		1.45%	(0.05%)
Average full-time equivalent employees	4,435	4,631	4,431	4,669