Asset Quality - Credit Risk Profile Based on Payment Activity (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	$ 53,101	$ 52,822	$ 49,605
Consumer Other - Key Community Bank [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	1,424	1,349	1,263
Consumer Other - Key Community Bank [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	1,421		1,261
Consumer Other - Key Community Bank [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	3		2
Credit Cards [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	701	729
Credit Cards [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	690
Credit Cards [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	11
Consumer Marine [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	1,160	1,358	1,542
Consumer Marine [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	1,130		1,523
Consumer Marine [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	30		19
Consumer Others [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	69	93	101
Consumer Others [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	68		100
Consumer Others [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	1		1
Consumer Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	16,078	15,942	15,002
Consumer Loans [Member] | Credit Risk Profile [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	3,354		2,906
Consumer Loans [Member] | Credit Risk Profile [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	3,309		2,884
Consumer Loans [Member] | Credit Risk Profile [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	$ 45		$ 22