Line of Business Results - Financial Information of Business Groups (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
SUMMARY OF OPERATIONS
Net interest income (TE)	$ 2,264	$ 2,267	$ 2,511
Noninterest income	1,967	1,808	1,954
Provision (credit) for loan and lease losses	229	(60)	638
Other noninterest expense	221	157	203
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	1,095	1,345	793
Allocated income taxes (benefit) and TE adjustments	(239)	(369)	(186)
Income (loss) from continuing operations	856	976	607
Income (loss) from discontinued operations, net of taxes	9	(44)	(23)
Net income (loss)	865	932	584
Less: Net income (loss) attributable to noncontrolling interests	7	12	30
NET INCOME (LOSS) ATTRIBUTABLE TO KEY	858	920	554
Key [Member]
SUMMARY OF OPERATIONS
Net interest income (TE)	2,288	2,292	2,537
Noninterest income	1,967	1,808	1,954
Total revenue (TE)	4,255	4,100	4,491
Provision (credit) for loan and lease losses	229	(60)	638
Depreciation and amortization expense	250	270	330
Other noninterest expense	2,657	2,520	2,704
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	1,119	1,370	819
Allocated income taxes (benefit) and TE adjustments	263	394	212
Income (loss) from continuing operations	856	976	607
Income (loss) from discontinued operations, net of taxes	9	(44)	(23)
Net income (loss)	865	932	584
Less: Net income (loss) attributable to noncontrolling interests	7	12	30
NET INCOME (LOSS) ATTRIBUTABLE TO KEY	858	920	554
AVERAGE BALANCES
Loans and leases	50,362	48,606	53,971
Total assets	80,891	82,093	87,474
Deposits	61,835	59,263	63,392
Net loan charge-offs	345	541	1,570
Return on average allocated equity	8.37%	9.51%	5.30%
Return on average allocated equity	8.46%	9.08%	5.08%
Average full-time equivalent employees	15,589	15,381	15,610
Other Segments [Member]
SUMMARY OF OPERATIONS
Net interest income (TE)	105	73	95
Noninterest income	344	234	327
Total revenue (TE)	449	307	422
Provision (credit) for loan and lease losses	50	(17)	260
Depreciation and amortization expense	9	18	38
Other noninterest expense	65	81	157
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	325	225	(33)
Allocated income taxes (benefit) and TE adjustments	76	39	(63)
Income (loss) from continuing operations	249	186	30
Net income (loss)	249	186	30
Less: Net income (loss) attributable to noncontrolling interests	4	11	31
NET INCOME (LOSS) ATTRIBUTABLE TO KEY	245	175	(1)
AVERAGE BALANCES
Loans and leases	3,612	4,842	6,513
Total assets	25,733	29,672	30,823
Deposits	428	725	1,597
Net loan charge-offs	77	117	454
Return on average allocated equity	37.01%	21.85%	(0.09%)
Return on average allocated equity	37.01%	21.85%	(0.09%)
Average full-time equivalent employees	5	24	187
Total Segments [Member]
SUMMARY OF OPERATIONS
Net interest income (TE)	2,281	2,272	2,515
Noninterest income	1,986	1,847	1,938
Total revenue (TE)	4,267	4,119	4,453
Provision (credit) for loan and lease losses	230	(55)	645
Depreciation and amortization expense	110	127	169
Other noninterest expense	2,803	2,677	2,842
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	1,124	1,370	797
Allocated income taxes (benefit) and TE adjustments	313	403	186
Income (loss) from continuing operations	811	967	611
Net income (loss)	811	967	611
Less: Net income (loss) attributable to noncontrolling interests	7	12	30
NET INCOME (LOSS) ATTRIBUTABLE TO KEY	804	955	581
AVERAGE BALANCES
Loans and leases	50,313	48,553	53,929
Total assets	80,241	80,964	85,426
Deposits	61,984	59,413	63,485
Net loan charge-offs	345	541	1,570
Return on average allocated equity	14.99%	15.23%	7.49%
Return on average allocated equity	14.99%	15.23%	7.49%
Average full-time equivalent employees	11,066	10,713	10,597
Reconciling Items [Member]
SUMMARY OF OPERATIONS
Net interest income (TE)	7	20	22
Noninterest income	(19)	(39)	16
Total revenue (TE)	(12)	(19)	38
Provision (credit) for loan and lease losses	(1)	(5)	(7)
Depreciation and amortization expense	140	143	161
Other noninterest expense	(146)	(157)	(138)
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	(5)		22
Allocated income taxes (benefit) and TE adjustments	(50)	(9)	26
Income (loss) from continuing operations	45	9	(4)
Income (loss) from discontinued operations, net of taxes	9	(44)	(23)
Net income (loss)	54	(35)	(27)
NET INCOME (LOSS) ATTRIBUTABLE TO KEY	54	(35)	(27)
AVERAGE BALANCES
Loans and leases	49	53	42
Total assets	650	1,129	2,048
Deposits	(149)	(150)	(93)
Return on average allocated equity	0.94%	0.23%	(0.13%)
Return on average allocated equity	1.13%	(0.91%)	(0.86%)
Average full-time equivalent employees	4,523	4,668	5,013
Key Community Bank [Member]
SUMMARY OF OPERATIONS
Net interest income (TE)	1,436	1,488	1,618
Noninterest income	773	746	772
Total revenue (TE)	2,209	2,234	2,390
Provision (credit) for loan and lease losses	156	160	413
Depreciation and amortization expense	55	38	37
Other noninterest expense	1,920	1,787	1,780
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	78	249	160
Allocated income taxes (benefit) and TE adjustments	(28)	37	5
Income (loss) from continuing operations	106	212	155
Income (loss) from discontinued operations, net of taxes
Net income (loss)	106	212	155
NET INCOME (LOSS) ATTRIBUTABLE TO KEY	106	212	155
AVERAGE BALANCES
Loans and leases	27,830	26,308	27,044
Total assets	31,519	29,744	30,254
Deposits	48,925	47,893	49,653
Net loan charge-offs	204	286	509
Return on average allocated equity	3.60%	6.62%	4.38%
Return on average allocated equity	3.60%	6.62%	4.38%
Average full-time equivalent employees	8,927	8,540	8,310
Key Corporate Bank [Member]
SUMMARY OF OPERATIONS
Net interest income (TE)	740	711	802
Noninterest income	869	867	839
Total revenue (TE)	1,609	1,578	1,641
Provision (credit) for loan and lease losses	24	(198)	(28)
Depreciation and amortization expense	46	71	94
Other noninterest expense	818	809	905
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	721	896	670
Allocated income taxes (benefit) and TE adjustments	265	327	244
Income (loss) from continuing operations	456	569	426
Income (loss) from discontinued operations, net of taxes
Net income (loss)	456	569	426
Less: Net income (loss) attributable to noncontrolling interests	3	1	(1)
NET INCOME (LOSS) ATTRIBUTABLE TO KEY	453	568	427
AVERAGE BALANCES
Loans and leases	18,871	17,403	20,372
Total assets	22,989	21,548	24,349
Deposits	12,631	10,795	12,235
Net loan charge-offs	$ 64	$ 138	$ 607
Return on average allocated equity	25.74%	25.04%	13.56%
Return on average allocated equity	25.74%	25.04%	13.56%
Average full-time equivalent employees	2,134	2,149	2,100