Asset Quality - Credit Risk Profile Based on Payment Activity (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	$ 52,822	$ 49,575
Consumer other - Key Community Bank [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	1,349	1,192
Credit cards [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	729
Consumer Marine [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	1,358	1,766
Consumer Others [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	93	125
Consumer loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	15,942	14,793
Performing [Member] | Consumer other - Key Community Bank [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	1,347	1,191
Performing [Member] | Credit cards [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	718
Performing [Member] | Consumer Marine [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	1,324	1,735
Performing [Member] | Consumer Others [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	91	124
Nonperforming [Member] | Consumer other - Key Community Bank [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	2	1
Nonperforming [Member] | Credit cards [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	11
Nonperforming [Member] | Consumer Marine [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	34	31
Nonperforming [Member] | Consumer Others [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	2	1
Credit Risk Profile [Member] | Consumer loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	3,529	3,083
Credit Risk Profile [Member] | Performing [Member] | Consumer loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	3,480	3,050
Credit Risk Profile [Member] | Nonperforming [Member] | Consumer loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	$ 49	$ 33