Asset Quality - Past Due Loans Including Current Loans (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 52,099	$ 51,623	$ 48,455
30 - 59 Days Past Due	183	286	245
60 - 89 Days Past Due	68	138	117
90 and Greater Days Past Due	80	78	131
Nonperforming Loans	652	674	657
Total Past Due and Nonperforming Loans	983	1,176	1,150
Purchased Credit Impaired	19	23
Total Loans	53,101	52,822	49,605
Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	23,512	23,030	20,678
30 - 59 Days Past Due	37	56	60
60 - 89 Days Past Due	9	34	13
90 and Greater Days Past Due	11	22	24
Nonperforming Loans	146	99	141
Total Past Due and Nonperforming Loans	203	211	238
Purchased Credit Impaired		1
Total Loans	23,715	23,242	20,916
Commercial Real Estate: Commercial Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	7,307	7,556	7,182
30 - 59 Days Past Due	16	21	15
60 - 89 Days Past Due	5	11	16
90 and Greater Days Past Due	38	9	24
Nonperforming Loans	106	120	172
Total Past Due and Nonperforming Loans	165	161	227
Purchased Credit Impaired	2	3
Total Loans	7,474	7,720	7,409
Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,031	943	1,033
30 - 59 Days Past Due	3	1	12
60 - 89 Days Past Due		2	24
90 and Greater Days Past Due		1	35
Nonperforming Loans	26	56	68
Total Past Due and Nonperforming Loans	29	60	139
Total Loans	1,060	1,003	1,172
Commercial Real Estate Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	8,338	8,499	8,215
30 - 59 Days Past Due	19	22	27
60 - 89 Days Past Due	5	13	40
90 and Greater Days Past Due	38	10	59
Nonperforming Loans	132	176	240
Total Past Due and Nonperforming Loans	194	221	366
Purchased Credit Impaired	2	3
Total Loans	8,534	8,723	8,581
Commercial Lease Financing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	4,734	4,772	5,051
30 - 59 Days Past Due	14	88	22
60 - 89 Days Past Due	7	31	8
90 and Greater Days Past Due	5	8	7
Nonperforming Loans	14	16	18
Total Past Due and Nonperforming Loans	40	143	55
Total Loans	4,774	4,915	5,106
Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	36,584	36,301	33,944
30 - 59 Days Past Due	70	166	109
60 - 89 Days Past Due	21	78	61
90 and Greater Days Past Due	54	40	90
Nonperforming Loans	292	291	399
Total Past Due and Nonperforming Loans	437	575	659
Purchased Credit Impaired	2	4
Total Loans	37,023	36,880	34,603
Real Estate - Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	2,037	2,023	1,895
30 - 59 Days Past Due	20	16	24
60 - 89 Days Past Due	7	10	10
90 and Greater Days Past Due	3	6	9
Nonperforming Loans	94	103	78
Total Past Due and Nonperforming Loans	124	135	121
Purchased Credit Impaired	15	16
Total Loans	2,176	2,174	2,016
Home Equity: Key Community Bank [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	9,877	9,506	9,361
30 - 59 Days Past Due	51	54	56
60 - 89 Days Past Due	25	26	26
90 and Greater Days Past Due	13	17	17
Nonperforming Loans	205	210	141
Total Past Due and Nonperforming Loans	294	307	240
Purchased Credit Impaired	2	3
Total Loans	10,173	9,816	9,601
Home Equity: Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	347	387	445
30 - 59 Days Past Due	7	9	10
60 - 89 Days Past Due	3	4	4
90 and Greater Days Past Due	2	2	3
Nonperforming Loans	16	21	17
Total Past Due and Nonperforming Loans	28	36	34
Total Loans	375	423	479
Home Equity Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	10,224	9,893	9,806
30 - 59 Days Past Due	58	63	66
60 - 89 Days Past Due	28	30	30
90 and Greater Days Past Due	15	19	20
Nonperforming Loans	221	231	158
Total Past Due and Nonperforming Loans	322	343	274
Purchased Credit Impaired	2	3
Total Loans	10,548	10,239	10,080
Consumer Other - Key Community Bank [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,403	1,325	1,237
30 - 59 Days Past Due	9	9	13
60 - 89 Days Past Due	3	5	4
90 and Greater Days Past Due	6	8	7
Nonperforming Loans	3	2	2
Total Past Due and Nonperforming Loans	21	24	26
Total Loans	1,424	1,349	1,263
Consumer Marine [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,106	1,288	1,478
30 - 59 Days Past Due	18	23	31
60 - 89 Days Past Due	5	9	10
90 and Greater Days Past Due	1	4	4
Nonperforming Loans	30	34	19
Total Past Due and Nonperforming Loans	54	70	64
Total Loans	1,160	1,358	1,542
Consumer Others [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	65	87	95
30 - 59 Days Past Due	2	2	2
60 - 89 Days Past Due		1	2
90 and Greater Days Past Due	1	1	1
Nonperforming Loans	1	2	1
Total Past Due and Nonperforming Loans	4	6	6
Total Loans	69	93	101
Consumer Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,171	1,375	1,573
30 - 59 Days Past Due	20	25	33
60 - 89 Days Past Due	5	10	12
90 and Greater Days Past Due	2	5	5
Nonperforming Loans	31	36	20
Total Past Due and Nonperforming Loans	58	76	70
Total Loans	1,229	1,451	1,643
Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	15,515	15,322	14,511
30 - 59 Days Past Due	113	120	136
60 - 89 Days Past Due	47	60	56
90 and Greater Days Past Due	26	38	41
Nonperforming Loans	360	383	258
Total Past Due and Nonperforming Loans	546	601	491
Purchased Credit Impaired	17	19
Total Loans	16,078	15,942	15,002
Credit Cards [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	680	706
30 - 59 Days Past Due	6	7
60 - 89 Days Past Due	4	5
Nonperforming Loans	11	11
Total Past Due and Nonperforming Loans	21	23
Total Loans	$ 701	$ 729