Asset Quality - Breakdown of Individually Impaired Loans (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Financing Receivable, Impaired [Line Items]
Recorded Investment	$ 411	$ 388
With related allowance recorded, Recorded Investment	153	170
Unpaid Principal Balance	639	751
With related allowance recorded, Unpaid Principal Balance	162	203
Specific Allowance	35	51
Average Recorded Investment	400	505
With related allowance recorded, Average Recorded Investment	162	201
With no related allowance recorded, Recorded Investment	258	218
With no related allowance recorded, Unpaid Principal Balance	477	548
With no related allowance recorded, Specific Allowance
With no related allowance recorded, Average Recorded Investment	238	304
Commercial, financial and agricultural [Member]
Financing Receivable, Impaired [Line Items]
With related allowance recorded, Recorded Investment	33	62
With related allowance recorded, Unpaid Principal Balance	42	70
Specific Allowance	12	26
With related allowance recorded, Average Recorded Investment	48	75
With no related allowance recorded, Recorded Investment	32	88
With no related allowance recorded, Unpaid Principal Balance	64	195
With no related allowance recorded, Specific Allowance
With no related allowance recorded, Average Recorded Investment	60	75
Commercial real estate: Commercial mortgage [Member]
Financing Receivable, Impaired [Line Items]
With related allowance recorded, Recorded Investment	7	96
With related allowance recorded, Unpaid Principal Balance	7	115
Specific Allowance	1	21
With related allowance recorded, Average Recorded Investment	51	91
With no related allowance recorded, Recorded Investment	89	100
With no related allowance recorded, Unpaid Principal Balance	142	240
With no related allowance recorded, Specific Allowance
With no related allowance recorded, Average Recorded Investment	95	131
Commercial real estate: Construction [Member]
Financing Receivable, Impaired [Line Items]
With related allowance recorded, Recorded Investment		12
With related allowance recorded, Unpaid Principal Balance		18
Specific Allowance		4
With related allowance recorded, Average Recorded Investment	6	29
With no related allowance recorded, Recorded Investment	48	30
With no related allowance recorded, Unpaid Principal Balance	182	113
With no related allowance recorded, Specific Allowance
With no related allowance recorded, Average Recorded Investment	39	98
Commercial real estate loans [Member]
Financing Receivable, Impaired [Line Items]
With related allowance recorded, Recorded Investment	7	108
With related allowance recorded, Unpaid Principal Balance	7	133
Specific Allowance	1	25
With related allowance recorded, Average Recorded Investment	57	120
With no related allowance recorded, Recorded Investment	137	130
With no related allowance recorded, Unpaid Principal Balance	324	353
With no related allowance recorded, Specific Allowance
With no related allowance recorded, Average Recorded Investment	134	229
Commercial loans [Member]
Financing Receivable, Impaired [Line Items]
With related allowance recorded, Recorded Investment	40
With related allowance recorded, Unpaid Principal Balance	49
Specific Allowance	13
With related allowance recorded, Average Recorded Investment	105
With no related allowance recorded, Recorded Investment	169
With no related allowance recorded, Unpaid Principal Balance	388
With no related allowance recorded, Specific Allowance
With no related allowance recorded, Average Recorded Investment	194
Real estate - residential mortgage [Member]
Financing Receivable, Impaired [Line Items]
With related allowance recorded, Recorded Investment	17
With related allowance recorded, Unpaid Principal Balance	17
Specific Allowance	1
With related allowance recorded, Average Recorded Investment	8
With no related allowance recorded, Recorded Investment	21
With no related allowance recorded, Unpaid Principal Balance	21
With no related allowance recorded, Specific Allowance
With no related allowance recorded, Average Recorded Investment	10
Home equity: Key Community Bank [Member]
Financing Receivable, Impaired [Line Items]
With related allowance recorded, Recorded Investment	22
With related allowance recorded, Unpaid Principal Balance	22
Specific Allowance	11
With related allowance recorded, Average Recorded Investment	11
With no related allowance recorded, Recorded Investment	65
With no related allowance recorded, Unpaid Principal Balance	65
With no related allowance recorded, Specific Allowance
With no related allowance recorded, Average Recorded Investment	33
Home equity: Other [Member]
Financing Receivable, Impaired [Line Items]
With related allowance recorded, Recorded Investment	9
With related allowance recorded, Unpaid Principal Balance	9
Specific Allowance	1
With related allowance recorded, Average Recorded Investment	5
With no related allowance recorded, Recorded Investment	3
With no related allowance recorded, Unpaid Principal Balance	3
With no related allowance recorded, Specific Allowance
With no related allowance recorded, Average Recorded Investment	1
Home equity loans [Member]
Financing Receivable, Impaired [Line Items]
With related allowance recorded, Recorded Investment	31
With related allowance recorded, Unpaid Principal Balance	31
Specific Allowance	12
With related allowance recorded, Average Recorded Investment	16
With no related allowance recorded, Recorded Investment	68
With no related allowance recorded, Unpaid Principal Balance	68
With no related allowance recorded, Specific Allowance
With no related allowance recorded, Average Recorded Investment	34
Consumer loans [Member]
Financing Receivable, Impaired [Line Items]
With related allowance recorded, Recorded Investment	113
With related allowance recorded, Unpaid Principal Balance	113
Specific Allowance	22
With related allowance recorded, Average Recorded Investment	57
With no related allowance recorded, Recorded Investment	89
With no related allowance recorded, Unpaid Principal Balance	89
With no related allowance recorded, Specific Allowance
With no related allowance recorded, Average Recorded Investment	44
Consumer other - Key Community Bank [Member]
Financing Receivable, Impaired [Line Items]
With related allowance recorded, Recorded Investment	2
With related allowance recorded, Unpaid Principal Balance	2
Specific Allowance	2
With related allowance recorded, Average Recorded Investment	1
Consumer Credit Card [Member]
Financing Receivable, Impaired [Line Items]
With related allowance recorded, Recorded Investment	2
With related allowance recorded, Unpaid Principal Balance	2
Specific Allowance
With related allowance recorded, Average Recorded Investment	1
Consumer Marine [Member]
Financing Receivable, Impaired [Line Items]
With related allowance recorded, Recorded Investment	60
With related allowance recorded, Unpaid Principal Balance	60
Specific Allowance	7
With related allowance recorded, Average Recorded Investment	30
Other Consumer [Member]
Financing Receivable, Impaired [Line Items]
With related allowance recorded, Recorded Investment	1
With related allowance recorded, Unpaid Principal Balance	1
Specific Allowance
With related allowance recorded, Average Recorded Investment	1
Consumer other [Member]
Financing Receivable, Impaired [Line Items]
With related allowance recorded, Recorded Investment	61
With related allowance recorded, Unpaid Principal Balance	61
Specific Allowance	7
With related allowance recorded, Average Recorded Investment	31
Commercial lease financing [Member]
Financing Receivable, Impaired [Line Items]
With related allowance recorded, Average Recorded Investment		$ 6