Asset Quality - Past Due Loans Including Current Loans (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 50,298		$ 46,811
30 to 59 Days Past Due	252		349
60 to 89 Days Past Due	102		129
90 and Greater Days Past Due	89		118
Nonperforming Loans	653	727	788
Total Past Due and Nonperforming Loans	1,096		1,384
Purchased Credit Impaired	25
Total Loans	51,419		48,195
Commercial, financial and agricultural [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	21,766		17,576
30 to 59 Days Past Due	46		40
60 to 89 Days Past Due	19		20
90 and Greater Days Past Due	15		24
Nonperforming Loans	132		188
Total Past Due and Nonperforming Loans	212		272
Purchased Credit Impaired	1
Total Loans	21,979		17,848
Commercial real estate: Commercial mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	7,344		7,612
30 to 59 Days Past Due	19		101
60 to 89 Days Past Due	3		3
90 and Greater Days Past Due	26		5
Nonperforming Loans	134		237
Total Past Due and Nonperforming Loans	182		346
Purchased Credit Impaired	3
Total Loans	7,529		7,958
Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	993		1,345
30 to 59 Days Past Due	5		5
60 to 89 Days Past Due	3		5
90 and Greater Days Past Due	13		8
Nonperforming Loans	53		93
Total Past Due and Nonperforming Loans	74		111
Total Loans	1,067		1,456
Commercial real estate loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	8,337		8,957
30 to 59 Days Past Due	24		106
60 to 89 Days Past Due	6		8
90 and Greater Days Past Due	39		13
Nonperforming Loans	187		330
Total Past Due and Nonperforming Loans	256		457
Purchased Credit Impaired	3
Total Loans	8,596		9,414
Commercial lease financing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	4,881		5,812
30 to 59 Days Past Due	48		57
60 to 89 Days Past Due	11		23
90 and Greater Days Past Due	2		34
Nonperforming Loans	18		31
Total Past Due and Nonperforming Loans	79		145
Total Loans	4,960		5,957
Commercial loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	34,984		32,345
30 to 59 Days Past Due	118		203
60 to 89 Days Past Due	36		51
90 and Greater Days Past Due	56		71
Nonperforming Loans	337		549
Total Past Due and Nonperforming Loans	547		874
Purchased Credit Impaired	4
Total Loans	35,535		33,219
Real estate - residential mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,997		1,747
30 to 59 Days Past Due	22		20
60 to 89 Days Past Due	13		11
90 and Greater Days Past Due	6		9
Nonperforming Loans	83		88
Total Past Due and Nonperforming Loans	124		128
Purchased Credit Impaired	17
Total Loans	2,138		1,875
Home equity: Key Community Bank [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	9,492		9,125
30 to 59 Days Past Due	57		63
60 to 89 Days Past Due	30		35
90 and Greater Days Past Due	15		22
Nonperforming Loans	171		102
Total Past Due and Nonperforming Loans	273		222
Purchased Credit Impaired	3
Total Loans	9,768		9,347
Home equity: Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	374		529
30 to 59 Days Past Due	9		13
60 to 89 Days Past Due	5		7
90 and Greater Days Past Due	3		4
Nonperforming Loans	18		12
Total Past Due and Nonperforming Loans	35		36
Total Loans	409		565
Home equity loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	9,866		9,654
30 to 59 Days Past Due	66		76
60 to 89 Days Past Due	35		42
90 and Greater Days Past Due	18		26
Nonperforming Loans	189		114
Total Past Due and Nonperforming Loans	308		258
Purchased Credit Impaired	3
Total Loans	10,177		9,912
Consumer other - Key Community Bank [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,290		1,159
30 to 59 Days Past Due	9		11
60 to 89 Days Past Due	4		5
90 and Greater Days Past Due	6		8
Nonperforming Loans	3		4
Total Past Due and Nonperforming Loans	22		28
Purchased Credit Impaired	1
Total Loans	1,313		1,187
Credit cards [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	692
30 to 59 Days Past Due	6
60 to 89 Days Past Due	4
Nonperforming Loans	8
Total Past Due and Nonperforming Loans	18
Total Loans	710
Consumer Marine [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,377		1,781
30 to 59 Days Past Due	29		36
60 to 89 Days Past Due	9		19
90 and Greater Days Past Due	2		3
Nonperforming Loans	31		32
Total Past Due and Nonperforming Loans	71		90
Total Loans	1,448		1,871
Consumer Others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	92		125
30 to 59 Days Past Due	2		3
60 to 89 Days Past Due	1		1
90 and Greater Days Past Due	1		1
Nonperforming Loans	2		1
Total Past Due and Nonperforming Loans	6		6
Total Loans	98		131
Consumer Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,469		1,906
30 to 59 Days Past Due	31		39
60 to 89 Days Past Due	10		20
90 and Greater Days Past Due	3		4
Nonperforming Loans	33		33
Total Past Due and Nonperforming Loans	77		96
Total Loans	1,546		2,002
Consumer loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	15,314		14,466
30 to 59 Days Past Due	134		146
60 to 89 Days Past Due	66		78
90 and Greater Days Past Due	33		47
Nonperforming Loans	316		239
Total Past Due and Nonperforming Loans	549		510
Purchased Credit Impaired	21
Total Loans	$ 15,884		$ 14,976