Line of Business Results (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2011		Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
SUMMARY OF OPERATIONS
Net interest income	$ 549		$ 640	$ 1,710	$ 1,882
Total noninterest income	483		486	1,394	1,428
Provision for loan and lease losses	10		94	(38)	735
Other noninterest expense	56		32	114	137
Income (loss) from continuing operations before income taxes (TE)	330		296	1,069	285
Allocated income taxes and TE adjustments	95		85	300	14
Income (loss) from continuing operations	235		211	769	271
Income (loss) from discontinued operations, net of taxes	(17)		15	(37)	(10)
Net income (loss)	218		226	732	261
Less: Net income (loss) attributable to noncontrolling interests	1		7	12	27
Net income (loss) attributable to Key	217		219	720	234
Line of Business Results (Textual) [Abstract]
Federal income tax rate				35.00%
State income tax rate				2.20%
Percentage of debt service provided by rental income from nonaffiliated third parties				at least 50% of the debt service is provided by rental income from nonaffiliated third parties
Community Banking [Member]
SUMMARY OF OPERATIONS
Net interest income	371		403	1,123	1,223
Total noninterest income	194		193	566	569
Total revenue (TE)	565		596	1,689	1,792
Provision for loan and lease losses	39		75	130	339
Depreciation and amortization expense	9		9	29	27
Other noninterest expense	447		450	1,320	1,334
Income (loss) from continuing operations before income taxes (TE)	70		62	210	92
Allocated income taxes and TE adjustments	12		9	37	(5)
Income (loss) from continuing operations	58		53	173	97
Net income (loss)	58		53	173	97
Net income (loss) attributable to Key	58		53	173	97
AVERAGE BALANCES
Loans and leases	26,270		26,772	26,275	27,249
Total assets	29,681		30,009	29,703	30,396
Deposits	47,672		48,682	47,831	50,167
OTHER FINANCIAL DATA
Net loan charge-offs	60		129	215	393
Return on average allocated equity	7.37%		6.08%	7.25%	3.68%
Return on average allocated equity, Total	7.37%		6.08%	7.25%	3.68%
Average full-time equivalent employees	8,641		8,303	8,509	8,242
Corporate Banking [Member]
SUMMARY OF OPERATIONS
Net interest income	170		199	528	592
Total noninterest income	198		225	631	610
Total revenue (TE)	368		424	1,159	1,202
Provision for loan and lease losses	(40)		(25)	(137)	235
Depreciation and amortization expense	17		24	56	73
Other noninterest expense	199		213	594	685
Income (loss) from continuing operations before income taxes (TE)	192		212	646	209
Allocated income taxes and TE adjustments	70		79	236	75
Income (loss) from continuing operations	122		133	410	134
Net income (loss)	122		133	410	134
Less: Net income (loss) attributable to noncontrolling interests			(1)	1	(1)
Net income (loss) attributable to Key	122		134	409	135
AVERAGE BALANCES
Loans and leases	16,985		19,540	17,274	20,966
Total assets	21,168		23,772	21,459	24,934
Deposits	10,544		11,565	10,671	12,056
OTHER FINANCIAL DATA
Net loan charge-offs	22		122	126	547
Return on average allocated equity	22.54%		17.73%	23.49%	5.62%
Return on average allocated equity, Total	22.54%		17.73%	23.49%	5.62%
Average full-time equivalent employees	2,288		2,210	2,212	2,200
Other Segments [Member]
SUMMARY OF OPERATIONS
Net interest income	12		39	63	66
Total noninterest income	93		75	209	247
Total revenue (TE)	105		114	272	313
Provision for loan and lease losses	10		44	(25)	172
Depreciation and amortization expense	4		9	15	33
Other noninterest expense	20		44	64	125
Income (loss) from continuing operations before income taxes (TE)	71		17	218	(17)
Allocated income taxes and TE adjustments	15		(8)	49	(42)
Income (loss) from continuing operations	56		25	169	25
Net income (loss)	56	[1]	25	169	25
Less: Net income (loss) attributable to noncontrolling interests	1		8	11	28
Net income (loss) attributable to Key	55		17	158	(3)
AVERAGE BALANCES
Loans and leases	4,678		6,213	4,980	6,766
Total assets	29,599		30,901	29,965	30,289
Deposits	817		1,698	796	1,743
OTHER FINANCIAL DATA
Net loan charge-offs	26		105	95	374
Return on average allocated equity	29.69%		6.79%	27.58%	(0.37%)
Return on average allocated equity, Total	29.69%		6.79%	27.58%	(0.37%)
Average full-time equivalent employees	6		180	31	190
Total Segments [Member]
SUMMARY OF OPERATIONS
Net interest income	553		641	1,714	1,881
Total noninterest income	485		493	1,406	1,426
Total revenue (TE)	1,038		1,134	3,120	3,307
Provision for loan and lease losses	9		94	(32)	746
Depreciation and amortization expense	30		42	100	133
Other noninterest expense	666		707	1,978	2,144
Income (loss) from continuing operations before income taxes (TE)	333		291	1,074	284
Allocated income taxes and TE adjustments	97		80	322	28
Income (loss) from continuing operations	236		211	752	256
Net income (loss)	236		211	752	256
Less: Net income (loss) attributable to noncontrolling interests	1		7	12	27
Net income (loss) attributable to Key	235		204	740	229
AVERAGE BALANCES
Loans and leases	47,933		52,525	48,529	54,981
Total assets	80,448		84,682	81,127	85,619
Deposits	59,033		61,945	59,298	63,966
OTHER FINANCIAL DATA
Net loan charge-offs	108		356	436	1,314
Return on average allocated equity	15.52%		10.86%	15.75%	3.91%
Return on average allocated equity, Total	15.52%		10.86%	15.75%	3.91%
Average full-time equivalent employees	10,935		10,693	10,752	10,632
Reconciling Items [Member]
SUMMARY OF OPERATIONS
Net interest income	2		6	15	21
Total noninterest income	(2)		(7)	(12)	2
Total revenue (TE)			(1)	3	23
Provision for loan and lease losses	1			(6)	(11)
Depreciation and amortization expense	35		39	108	121
Other noninterest expense	(39)		(52)	(113)	(108)
Income (loss) from continuing operations before income taxes (TE)	3		12	14	21
Allocated income taxes and TE adjustments	4		12	(3)	6
Income (loss) from continuing operations	(1)			17	15
Income (loss) from discontinued operations, net of taxes	(17)		15	(37)	(10)
Net income (loss)	(18)		15	(20)	5
Net income (loss) attributable to Key	(18)		15	(20)	5
AVERAGE BALANCES
Loans and leases	75		41	57	49
Total assets	1,011		2,045	1,242	2,139
Deposits	(133)		(87)	(142)	(103)
OTHER FINANCIAL DATA
Net loan charge-offs	1		1
Return on average allocated equity	(0.10%)			0.58%	0.67%
Return on average allocated equity, Total	(1.87%)		1.68%	(0.68%)	0.22%
Average full-time equivalent employees	4,555		4,891	4,629	5,041
Key [Member]
SUMMARY OF OPERATIONS
Net interest income	555		647	1,729	1,902
Total noninterest income	483		486	1,394	1,428
Total revenue (TE)	1,038		1,133	3,123	3,330
Provision for loan and lease losses	10		94	(38)	735
Depreciation and amortization expense	65		81	208	254
Other noninterest expense	627		655	1,865	2,036
Income (loss) from continuing operations before income taxes (TE)	336		303	1,088	305
Allocated income taxes and TE adjustments	101		92	319	34
Income (loss) from continuing operations	235		211	769	271
Income (loss) from discontinued operations, net of taxes	(17)		15	(37)	(10)
Net income (loss)	218		226	732	261
Less: Net income (loss) attributable to noncontrolling interests	1		7	12	27
Net income (loss) attributable to Key	217		219	720	234
AVERAGE BALANCES
Loans and leases	48,008		52,566	48,586	55,030
Total assets	81,459		86,727	82,369	87,758
Deposits	58,900		61,858	59,156	63,863
OTHER FINANCIAL DATA
Net loan charge-offs	$ 109		$ 357	$ 436	$ 1,314
Return on average allocated equity	9.44%		7.36%	9.93%	3.02%
Return on average allocated equity, Total	8.76%		7.90%	9.44%	2.90%
Average full-time equivalent employees	15,490		15,584	15,381	15,673

[1] See Key's Consolidated Statements of Changes in Equity