Line of Business Results - Financial Information of Business Groups (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Segment Reporting Information [Line Items]
Net interest income (TE)	$ 578	$ 572	$ 1,742	$ 1,663
Noninterest income	459	518	1,313	1,417
Provision (credit) for loan and lease losses	28	109	111	172
Other noninterest expense	83	91	249	264
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	293	269	836	824
Allocated income taxes and TE adjustments	59	51	201	178
Income (loss) from continuing operations	234	218	635	646
Income (loss) from discontinued operations, net of taxes	37	3	45	16
Net income (loss)	271	221	680	662
Less: Net income (loss) attributable to noncontrolling interests	(1)	2		7
Net income (loss) attributable to Key	272	219	680	655
OTHER FINANCIAL DATA
Net loan charge-offs		45
Key [Member]
Segment Reporting Information [Line Items]
Net interest income (TE)	584	578	1,759	1,681
Noninterest income	459	518	1,313	1,417
Total revenue (TE)	1,043	1,096	3,072	3,098
Provision (credit) for loan and lease losses	28	109	111	172
Depreciation and amortization expense	64	64	195	183
Other noninterest expense	652	648	1,913	1,901
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	299	275	853	842
Allocated income taxes and TE adjustments	65	57	218	196
Income (loss) from continuing operations	234	218	635	646
Income (loss) from discontinued operations, net of taxes	37	3	45	16
Net income (loss)	271	221	680	662
Less: Net income (loss) attributable to noncontrolling interests	(1)	2		7
Net income (loss) attributable to Key	272	219	680	655
AVERAGE BALANCES
Loans and leases	53,271	50,695	52,867	49,860
Total assets	83,509	80,805	83,427	80,704
Deposits	65,983	62,676	65,029	61,129
OTHER FINANCIAL DATA
Net loan charge-offs	37	109	131	287
Return on average allocated equity	9.11%	8.41%	8.23%	8.43%
Return on average allocated equity	10.54%	8.52%	8.82%	8.64%
Average full-time equivalent employees	14,555	15,833	14,980	15,565
Key Community Bank [Member]
Segment Reporting Information [Line Items]
Net interest income (TE)	357	376	1,075	1,089
Noninterest income	194	199	582	556
Total revenue (TE)	551	575	1,657	1,645
Provision (credit) for loan and lease losses	24	123	123	124
Depreciation and amortization expense	19	16	58	35
Other noninterest expense	422	462	1,280	1,333
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	86	(26)	196	153
Allocated income taxes and TE adjustments	32	(10)	73	57
Income (loss) from continuing operations	54	(16)	123	96
Income (loss) from discontinued operations, net of taxes
Net income (loss)	54	(16)	123	96
Less: Net income (loss) attributable to noncontrolling interests
Net income (loss) attributable to Key	54	(16)	123	96
AVERAGE BALANCES
Loans and leases	29,495	27,764	29,213	26,720
Total assets	31,679	30,305	31,575	29,076
Deposits	49,652	49,269	49,492	48,242
OTHER FINANCIAL DATA
Net loan charge-offs	27	91	116	184
Return on average allocated equity	7.49%	(2.25%)	5.74%	4.56%
Return on average allocated equity	7.49%	(2.25%)	5.74%	4.56%
Average full-time equivalent employees	7,990	9,064	8,336	8,756
Key Corporate Bank [Member]
Segment Reporting Information [Line Items]
Net interest income (TE)	188	189	565	575
Noninterest income	189	181	567	543
Total revenue (TE)	377	370	1,132	1,118
Provision (credit) for loan and lease losses	13	(3)	7	14
Depreciation and amortization expense	10	12	33	43
Other noninterest expense	207	189	596	593
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	147	172	496	468
Allocated income taxes and TE adjustments	51	63	179	171
Income (loss) from continuing operations	96	109	317	297
Income (loss) from discontinued operations, net of taxes
Net income (loss)	96	109	317	297
Less: Net income (loss) attributable to noncontrolling interests				3
Net income (loss) attributable to Key	96	109	317	294
AVERAGE BALANCES
Loans and leases	20,586	18,893	20,256	18,677
Total assets	24,487	22,912	24,108	22,826
Deposits	16,125	12,879	15,241	12,287
OTHER FINANCIAL DATA
Net loan charge-offs	7	8		43
Return on average allocated equity	23.31%	26.06%	26.07%	22.48%
Return on average allocated equity	23.31%	26.06%	26.07%	22.48%
Average full-time equivalent employees	2,018	2,009	1,968	2,023
Other Segments [Member]
Segment Reporting Information [Line Items]
Net interest income (TE)	40	11	120	10
Noninterest income	74	146	163	336
Total revenue (TE)	114	157	283	346
Provision (credit) for loan and lease losses	(8)	(11)	(19)	35
Depreciation and amortization expense	2	2	5	7
Other noninterest expense	14	33	49	82
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	106	133	248	222
Allocated income taxes and TE adjustments	15	27	18	15
Income (loss) from continuing operations	91	106	230	207
Income (loss) from discontinued operations, net of taxes
Net income (loss)	91	106	230	207
Less: Net income (loss) attributable to noncontrolling interests	(1)	2		4
Net income (loss) attributable to Key	92	104	230	203
AVERAGE BALANCES
Loans and leases	3,123	3,980	3,342	4,408
Total assets	26,899	27,020	27,210	28,120
Deposits	754	669	713	743
OTHER FINANCIAL DATA
Net loan charge-offs	3	9	15	61
Return on average allocated equity	55.73%	53.32%	44.83%	33.44%
Return on average allocated equity	55.73%	53.32%	44.83%	33.44%
Average full-time equivalent employees	55	53	53	53
Total Segments [Member]
Segment Reporting Information [Line Items]
Net interest income (TE)	585	576	1,760	1,674
Noninterest income	457	526	1,312	1,435
Total revenue (TE)	1,042	1,102	3,072	3,109
Provision (credit) for loan and lease losses	29	109	111	173
Depreciation and amortization expense	31	30	96	85
Other noninterest expense	643	684	1,925	2,008
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	339	279	940	843
Allocated income taxes and TE adjustments	98	80	270	243
Income (loss) from continuing operations	241	199	670	600
Income (loss) from discontinued operations, net of taxes
Net income (loss)	241	199	670	600
Less: Net income (loss) attributable to noncontrolling interests	(1)	2		7
Net income (loss) attributable to Key	242	197	670	593
AVERAGE BALANCES
Loans and leases	53,204	50,637	52,811	49,805
Total assets	83,065	80,237	82,893	80,022
Deposits	66,531	62,817	65,446	61,272
OTHER FINANCIAL DATA
Net loan charge-offs	37	108	131	288
Return on average allocated equity	18.65%	14.87%	17.30%	14.74%
Return on average allocated equity	18.65%	14.87%	17.30%	14.74%
Average full-time equivalent employees	10,063	11,126	10,357	10,832
Reconciling Items [Member]
Segment Reporting Information [Line Items]
Net interest income (TE)	(1)	2	(1)	7
Noninterest income	2	(8)	1	(18)
Total revenue (TE)	1	(6)		(11)
Provision (credit) for loan and lease losses	(1)			(1)
Depreciation and amortization expense	33	34	99	98
Other noninterest expense	9	(36)	(12)	(107)
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	(40)	(4)	(87)	(1)
Allocated income taxes and TE adjustments	(33)	(23)	(52)	(47)
Income (loss) from continuing operations	(7)	19	(35)	46
Income (loss) from discontinued operations, net of taxes	37	3	45	16
Net income (loss)	30	22	10	62
Less: Net income (loss) attributable to noncontrolling interests
Net income (loss) attributable to Key	30	22	10	62
AVERAGE BALANCES
Loans and leases	67	58	56	55
Total assets	444	568	534	682
Deposits	(548)	(141)	(417)	(143)
OTHER FINANCIAL DATA
Net loan charge-offs		$ 1		$ (1)
Return on average allocated equity	(0.55%)	1.53%	(0.91%)	1.29%
Return on average allocated equity	2.34%	1.77%	0.26%	1.74%
Average full-time equivalent employees	4,492	4,707	4,623	4,757