Line of Business Results - Financial Information of Business Groups (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Segment Reporting Information [Line Items]
Net interest income (TE)	$ 581	$ 538	$ 1,164	$ 1,091
Noninterest income	429	457	854	899
Provision (credit) for loan and lease losses	28	21	83	63
Other noninterest expense	(84)	(79)	(166)	(173)
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	271	281	543	555
Allocated income taxes and TE adjustments	72	54	142	127
Income (loss) from continuing operations	199	227	401	428
Income (loss) from discontinued operations, net of taxes	5	14	8	13
Net income (loss)	204	241	409	441
Less: Net income (loss) attributable to noncontrolling interests		5	1	5
Net income (loss) attributable to Key	204	236	408	436
Key [Member]
Segment Reporting Information [Line Items]
Net interest income (TE)	586	544	1,175	1,103
Noninterest income	429	457	854	899
Total revenue (TE)	1,015	1,001	2,029	2,002
Provision (credit) for loan and lease losses	28	21	83	63
Depreciation and amortization expense	65	59	131	131
Other noninterest expense	646	634	1,261	1,241
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	276	287	554	567
Allocated income taxes and TE adjustments	77	60	153	139
Income (loss) from continuing operations	199	227	401	428
Income (loss) from discontinued operations, net of taxes	5	14	8	13
Net income (loss)	204	241	409	441
Less: Net income (loss) attributable to noncontrolling interests		5	1	5
Net income (loss) attributable to Key	204	236	408	436
AVERAGE BALANCES
Loans and leases	52,696	49,446	52,661	49,438
Total assets	84,048	80,880	83,385	80,652
Deposits	65,441	61,063	64,543	60,347
OTHER FINANCIAL DATA
Net loan charge-offs	45	77	94	178
Return on average allocated equity	7.74%	8.84%	7.81%	8.47%
Return on average allocated equity	7.93%	9.40%	7.96%	8.73%
Average full-time equivalent employees	14,999	15,455	15,197	15,430
Key Community Bank [Member]
Segment Reporting Information [Line Items]
Net interest income (TE)	357	356	719	713
Noninterest income	198	181	385	356
Total revenue (TE)	555	537	1,104	1,069
Provision (credit) for loan and lease losses	41	(4)	99
Depreciation and amortization expense	19	9	39	19
Other noninterest expense	437	446	858	873
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	58	86	108	177
Allocated income taxes and TE adjustments	22	32	40	66
Income (loss) from continuing operations	36	54	68	111
Income (loss) from discontinued operations, net of taxes
Net income (loss)	36	54	68	111
Net income (loss) attributable to Key	36	54	68	111
AVERAGE BALANCES
Loans and leases	29,161	26,413	29,069	26,193
Total assets	31,570	28,695	31,522	28,454
Deposits	49,473	47,946	49,411	47,723
OTHER FINANCIAL DATA
Net loan charge-offs	42	46	89	92
Return on average allocated equity	5.02%	7.82%	4.77%	7.93%
Return on average allocated equity	5.02%	7.82%	4.77%	7.93%
Average full-time equivalent employees	8,437	8,742	8,632	8,724
Key Corporate Bank [Member]
Segment Reporting Information [Line Items]
Net interest income (TE)	189	190	376	386
Noninterest income	187	181	380	364
Total revenue (TE)	376	371	756	750
Provision (credit) for loan and lease losses	(10)	4	(6)	17
Depreciation and amortization expense	11	15	23	31
Other noninterest expense	191	198	389	405
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	184	154	350	297
Allocated income taxes and TE adjustments	67	56	128	108
Income (loss) from continuing operations	117	98	222	189
Income (loss) from discontinued operations, net of taxes
Net income (loss)	117	98	222	189
Less: Net income (loss) attributable to noncontrolling interests		3		3
Net income (loss) attributable to Key	117	95	222	186
AVERAGE BALANCES
Loans and leases	20,133	18,541	20,089	18,568
Total assets	23,965	22,709	23,915	22,783
Deposits	15,606	12,414	14,792	11,987
OTHER FINANCIAL DATA
Net loan charge-offs	(6)	9	(7)	34
Return on average allocated equity	28.79%	22.00%	27.58%	20.91%
Return on average allocated equity	28.79%	22.00%	27.58%	20.91%
Average full-time equivalent employees	1,950	2,028	1,938	2,025
Other Segments [Member]
Segment Reporting Information [Line Items]
Net interest income (TE)	40	(4)	79	(1)
Noninterest income	46	98	90	189
Total revenue (TE)	86	94	169	188
Provision (credit) for loan and lease losses	(4)	21	(12)	46
Depreciation and amortization expense	2	2	3	5
Other noninterest expense	17	23	36	48
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	71	48	142	89
Allocated income taxes and TE adjustments	1	(3)	3	(13)
Income (loss) from continuing operations	70	51	139	102
Net income (loss)	70	51	139	102
Less: Net income (loss) attributable to noncontrolling interests		2	1	2
Net income (loss) attributable to Key	70	49	138	100
AVERAGE BALANCES
Loans and leases	3,348	4,425	3,454	4,624
Total assets	27,936	28,797	27,369	28,676
Deposits	758	811	692	780
OTHER FINANCIAL DATA
Net loan charge-offs	9	22	12	51
Return on average allocated equity	40.63%	24.21%	39.64%	24.26%
Return on average allocated equity	40.63%	24.21%	39.64%	24.26%
Average full-time equivalent employees	54	54	52	53
Total Segments [Member]
Segment Reporting Information [Line Items]
Net interest income (TE)	586	542	1,174	1,098
Noninterest income	431	460	855	909
Total revenue (TE)	1,017	1,002	2,029	2,007
Provision (credit) for loan and lease losses	27	21	81	63
Depreciation and amortization expense	32	26	65	55
Other noninterest expense	645	667	1,283	1,326
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	313	288	600	563
Allocated income taxes and TE adjustments	90	85	171	161
Income (loss) from continuing operations	223	203	429	402
Net income (loss)	223	203	429	402
Less: Net income (loss) attributable to noncontrolling interests		5	1	5
Net income (loss) attributable to Key	223	198	428	397
AVERAGE BALANCES
Loans and leases	52,642	49,379	52,612	49,385
Total assets	83,471	80,201	82,806	79,913
Deposits	65,837	61,171	64,895	60,490
OTHER FINANCIAL DATA
Net loan charge-offs	45	77	94	177
Return on average allocated equity	17.22%	14.94%	16.60%	14.70%
Return on average allocated equity	17.22%	14.94%	16.60%	14.70%
Average full-time equivalent employees	10,441	10,824	10,622	10,802
Reconciling Items [Member]
Segment Reporting Information [Line Items]
Net interest income (TE)		2	1	5
Noninterest income	(2)	(3)	(1)	(10)
Total revenue (TE)	(2)	(1)		(5)
Provision (credit) for loan and lease losses	1		2
Depreciation and amortization expense	33	33	66	76
Other noninterest expense	1	(33)	(22)	(85)
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	(37)	(1)	(46)	4
Allocated income taxes and TE adjustments	(13)	(25)	(18)	(22)
Income (loss) from continuing operations	(24)	24	(28)	26
Income (loss) from discontinued operations, net of taxes	5	14	8	13
Net income (loss)	(19)	38	(20)	39
Net income (loss) attributable to Key	(19)	38	(20)	39
AVERAGE BALANCES
Loans and leases	54	67	49	53
Total assets	577	679	579	739
Deposits	(396)	(108)	(352)	(143)
OTHER FINANCIAL DATA
Net loan charge-offs				$ 1
Return on average allocated equity	(1.88%)	2.02%	(1.10%)	1.13%
Return on average allocated equity	(1.49%)	3.20%	(0.79%)	1.70%
Average full-time equivalent employees	4,558	4,631	4,575	4,628