Asset Quality - Past Due Loans Including Current Loans (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 54,624	$ 53,544	$ 51,451
30 - 59 Days Past Due	186	213	217
60 - 89 Days Past Due	81	105	151
90 and Greater Days Past Due	89	71	83
Nonperforming Loans	449	508	650
Total Past Due and Nonperforming Loans	805	897	1,101
Purchased Credit Impaired	16	16	22
Total Loans	55,445	54,457	52,574
Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	39,202	37,992	36,254
30 - 59 Days Past Due	94	101	109
60 - 89 Days Past Due	32	48	99
90 and Greater Days Past Due	49	38	49
Nonperforming Loans	126	147	295
Total Past Due and Nonperforming Loans	301	334	552
Purchased Credit Impaired	1	1	3
Total Loans	39,504	38,327	36,809
Credit Cards [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	671	698	668
30 - 59 Days Past Due	7	11	8
60 - 89 Days Past Due	4	5	4
90 and Greater Days Past Due	15	4
Nonperforming Loans	1	4	13
Total Past Due and Nonperforming Loans	27	24	25
Purchased Credit Impaired
Total Loans	698	722	693
Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	26,071	24,823	23,134
30 - 59 Days Past Due	67	39	35
60 - 89 Days Past Due	8	8	74
90 and Greater Days Past Due	18	16	26
Nonperforming Loans	60	77	142
Total Past Due and Nonperforming Loans	153	140	277
Purchased Credit Impaired			1
Total Loans	26,224	24,963	23,412
Commercial Real Estate: Commercial Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	7,806	7,638	7,368
30 - 59 Days Past Due	9	20	35
60 - 89 Days Past Due	7	7	14
90 and Greater Days Past Due	17	17	11
Nonperforming Loans	37	37	114
Total Past Due and Nonperforming Loans	70	81	174
Purchased Credit Impaired	1	1	2
Total Loans	7,877	7,720	7,544
Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	987	1,068	1,024
30 - 59 Days Past Due	3	10	5
60 - 89 Days Past Due	5
90 and Greater Days Past Due	1	1	1
Nonperforming Loans	11	14	27
Total Past Due and Nonperforming Loans	20	25	33
Purchased Credit Impaired
Total Loans	1,007	1,093	1,057
Commercial Real Estate Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	8,793	8,706	8,392
30 - 59 Days Past Due	12	30	40
60 - 89 Days Past Due	12	7	14
90 and Greater Days Past Due	18	18	12
Nonperforming Loans	48	51	141
Total Past Due and Nonperforming Loans	90	106	207
Purchased Credit Impaired	1	1	2
Total Loans	8,884	8,813	8,601
Commercial Lease Financing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	4,338	4,463	4,728
30 - 59 Days Past Due	15	32	34
60 - 89 Days Past Due	12	33	11
90 and Greater Days Past Due	13	4	11
Nonperforming Loans	18	19	12
Total Past Due and Nonperforming Loans	58	88	68
Purchased Credit Impaired
Total Loans	4,396	4,551	4,796
Real Estate - Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	2,043	2,038	2,037
30 - 59 Days Past Due	13	19	15
60 - 89 Days Past Due	6	5	5
90 and Greater Days Past Due	3	4	7
Nonperforming Loans	105	107	96
Total Past Due and Nonperforming Loans	127	135	123
Purchased Credit Impaired	13	14	16
Total Loans	2,183	2,187	2,176
Home Equity: Key Community Bank [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	10,010	10,038	9,512
30 - 59 Days Past Due	45	51	51
60 - 89 Days Past Due	25	31	28
90 and Greater Days Past Due	11	14	17
Nonperforming Loans	188	205	199
Total Past Due and Nonperforming Loans	269	301	295
Purchased Credit Impaired	2	1	2
Total Loans	10,281	10,340	9,809
Home Equity: Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	296	308	371
30 - 59 Days Past Due	5	6	7
60 - 89 Days Past Due	2	4	3
90 and Greater Days Past Due	1	1	2
Nonperforming Loans	11	15	18
Total Past Due and Nonperforming Loans	19	26	30
Purchased Credit Impaired
Total Loans	315	334	401
Home Equity Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	10,306	10,346	9,883
30 - 59 Days Past Due	50	57	58
60 - 89 Days Past Due	27	35	31
90 and Greater Days Past Due	12	15	19
Nonperforming Loans	199	220	217
Total Past Due and Nonperforming Loans	288	327	325
Purchased Credit Impaired	2	1	2
Total Loans	10,596	10,674	10,210
Consumer Other - Key Community Bank [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,415	1,426	1,331
30 - 59 Days Past Due	8	8	8
60 - 89 Days Past Due	5	5	4
90 and Greater Days Past Due	6	7	6
Nonperforming Loans	2	3	3
Total Past Due and Nonperforming Loans	21	23	21
Purchased Credit Impaired			1
Total Loans	1,436	1,449	1,353
Consumer Marine [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	928	979	1,202
30 - 59 Days Past Due	12	15	18
60 - 89 Days Past Due	6	6	7
90 and Greater Days Past Due	4	2	2
Nonperforming Loans	15	26	25
Total Past Due and Nonperforming Loans	37	49	52
Purchased Credit Impaired
Total Loans	965	1,028	1,254
Consumer Others [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	59	65	76
30 - 59 Days Past Due	2	2	1
60 - 89 Days Past Due	1	1	1
90 and Greater Days Past Due		1
Nonperforming Loans	1	1	1
Total Past Due and Nonperforming Loans	4	5	3
Purchased Credit Impaired
Total Loans	63	70	79
Consumer Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	987	1,044	1,278
30 - 59 Days Past Due	14	17	19
60 - 89 Days Past Due	7	7	8
90 and Greater Days Past Due	4	3	2
Nonperforming Loans	16	27	26
Total Past Due and Nonperforming Loans	41	54	55
Purchased Credit Impaired
Total Loans	1,028	1,098	1,333
Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	15,422	15,552	15,197
30 - 59 Days Past Due	92	112	108
60 - 89 Days Past Due	49	57	52
90 and Greater Days Past Due	40	33	34
Nonperforming Loans	323	361	355
Total Past Due and Nonperforming Loans	504	563	549
Purchased Credit Impaired	15	15	19
Total Loans	$ 15,941	$ 16,130	$ 15,765