Line of Business Results (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
SUMMARY OF OPERATIONS
Net interest income (TE)	$ 553	$ 597
Noninterest income	472	457
Provision (credit) for loan and lease losses	42	(40)
Other noninterest expense	33	17
Income (loss) from continuing operations before income taxes (TE)	280	393
Allocated income taxes and TE adjustments	75	111
Income (loss) from continuing operations	205	282
Income (loss) from discontinued operations, net of taxes	(5)	(11)
NET INCOME (LOSS)	200	271
Less: Net income (loss) attributable to noncontrolling interests		8
NET INCOME (LOSS) ATTRIBUTABLE TO KEY	200	263
Parent [Member]
SUMMARY OF OPERATIONS
Net interest income (TE)	559	604
Noninterest income	472	457
Total revenue (TE)	1,031	1,061
Provision (credit) for loan and lease losses	42	(40)
Depreciation and amortization expense	60	74
Other noninterest expense	643	627
Income (loss) from continuing operations before income taxes (TE)	286	400
Allocated income taxes and TE adjustments	81	118
Income (loss) from continuing operations	205	282
Income (loss) from discontinued operations, net of taxes	(5)	(11)
NET INCOME (LOSS)	200	271
Less: Net income (loss) attributable to noncontrolling interests		8
NET INCOME (LOSS) ATTRIBUTABLE TO KEY	200	263
AVERAGE BALANCES
Loans and leases	49,430	49,312
Total assets	80,466	84,295
Deposits	59,631	60,040
OTHER FINANCIAL DATA
Net loan charge-offs	101	193
Return on average allocated equity	8.25%	9.91%
Return on average allocated equity, Total	8.05%	9.51%
Average full-time equivalent employees	15,404	15,301
Community Bank [Member]
SUMMARY OF OPERATIONS
Net interest income (TE)	353	378
Noninterest income	175	187
Total revenue (TE)	528	565
Provision (credit) for loan and lease losses	2	11
Depreciation and amortization expense	9	10
Other noninterest expense	447	437
Income (loss) from continuing operations before income taxes (TE)	70	107
Allocated income taxes and TE adjustments	13	26
Income (loss) from continuing operations	57	81
Income (loss) from discontinued operations, net of taxes
NET INCOME (LOSS)	57	81
Less: Net income (loss) attributable to noncontrolling interests
NET INCOME (LOSS) ATTRIBUTABLE TO KEY	57	81
AVERAGE BALANCES
Loans and leases	26,617	26,312
Total assets	30,194	29,739
Deposits	47,768	48,108
OTHER FINANCIAL DATA
Net loan charge-offs	49	76
Return on average allocated equity	7.74%	9.97%
Return on average allocated equity, Total	7.74%	9.97%
Average full-time equivalent employees	8,719	8,378
Key Corporate Banking [Member]
SUMMARY OF OPERATIONS
Net interest income (TE)	187	187
Noninterest income	214	219
Total revenue (TE)	401	406
Provision (credit) for loan and lease losses	13	(21)
Depreciation and amortization expense	13	20
Other noninterest expense	218	208
Income (loss) from continuing operations before income taxes (TE)	157	199
Allocated income taxes and TE adjustments	57	73
Income (loss) from continuing operations	100	126
Income (loss) from discontinued operations, net of taxes
NET INCOME (LOSS)	100	126
Less: Net income (loss) attributable to noncontrolling interests
NET INCOME (LOSS) ATTRIBUTABLE TO KEY	100	126
AVERAGE BALANCES
Loans and leases	18,584	17,677
Total assets	22,863	21,747
Deposits	11,556	11,282
OTHER FINANCIAL DATA
Net loan charge-offs	25	75
Return on average allocated equity	21.07%	19.71%
Return on average allocated equity, Total	21.07%	19.71%
Average full-time equivalent employees	2,254	2,155
Other Segments [Member]
SUMMARY OF OPERATIONS
Net interest income (TE)	15	32
Noninterest income	90	61
Total revenue (TE)	105	93
Provision (credit) for loan and lease losses	27	(25)
Depreciation and amortization expense	3	6
Other noninterest expense	21	23
Income (loss) from continuing operations before income taxes (TE)	54	89
Allocated income taxes and TE adjustments	9	23
Income (loss) from continuing operations	45	66
Income (loss) from discontinued operations, net of taxes
NET INCOME (LOSS)	45	66
Less: Net income (loss) attributable to noncontrolling interests		8
NET INCOME (LOSS) ATTRIBUTABLE TO KEY	45	58
AVERAGE BALANCES
Loans and leases	4,189	5,294
Total assets	26,584	31,362
Deposits	487	770
OTHER FINANCIAL DATA
Net loan charge-offs	27	42
Return on average allocated equity	25.93%	28.20%
Return on average allocated equity, Total	25.93%	28.20%
Average full-time equivalent employees	5	64
Total Segments [Member]
SUMMARY OF OPERATIONS
Net interest income (TE)	555	597
Noninterest income	479	467
Total revenue (TE)	1,034	1,064
Provision (credit) for loan and lease losses	42	(35)
Depreciation and amortization expense	25	36
Other noninterest expense	686	668
Income (loss) from continuing operations before income taxes (TE)	281	395
Allocated income taxes and TE adjustments	79	122
Income (loss) from continuing operations	202	273
Income (loss) from discontinued operations, net of taxes
NET INCOME (LOSS)	202	273
Less: Net income (loss) attributable to noncontrolling interests		8
NET INCOME (LOSS) ATTRIBUTABLE TO KEY	202	265
AVERAGE BALANCES
Loans and leases	49,390	49,283
Total assets	79,641	82,848
Deposits	59,811	60,160
OTHER FINANCIAL DATA
Net loan charge-offs	101	193
Return on average allocated equity	14.59%	15.99%
Return on average allocated equity, Total	14.59%	15.99%
Average full-time equivalent employees	10,978	10,597
Reconciling Items [Member]
SUMMARY OF OPERATIONS
Net interest income (TE)	4	7
Noninterest income	(7)	(10)
Total revenue (TE)	(3)	(3)
Provision (credit) for loan and lease losses	0	(5)
Depreciation and amortization expense	35	38
Other noninterest expense	(43)	(41)
Income (loss) from continuing operations before income taxes (TE)	5	5
Allocated income taxes and TE adjustments	2	(4)
Income (loss) from continuing operations	3	9
Income (loss) from discontinued operations, net of taxes	(5)	(11)
NET INCOME (LOSS)	(2)	(2)
Less: Net income (loss) attributable to noncontrolling interests
NET INCOME (LOSS) ATTRIBUTABLE TO KEY	(2)	(2)
AVERAGE BALANCES
Loans and leases	40	29
Total assets	825	1,447
Deposits	(180)	(120)
OTHER FINANCIAL DATA
Net loan charge-offs
Return on average allocated equity	0.27%	0.81%
Return on average allocated equity, Total	(0.18%)	(0.18%)
Average full-time equivalent employees	4,426	4,704