Asset Quality - Changes in Allowance for Loan and Lease Losses by Loan Category (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations	$ 888	$ 1,004
Provision	54	41
Charge-offs	(90)	(132)
Recoveries	41	31
Balance at end of period - continuing operations	893	944
Discontinued Operations, Beginning Balance	55	104
Provision, Discontinued Operations	6	5
Charge-offs, Discontinued Operations	(16)	(23)
Recoveries, Discontinued Operations	4	4
Discontinued Operations, Ending Balance	49	90
Financing Receivable Allowance For Credit Losses Total ALLL Including Discontinued Operations, Beginning Balance	943	1,108
Provisions, Total ALLL - Including Discontinued Operations	60	46
Charge-offs, Total ALLL - Including Discontinued Operations	(106)	(155)
Recoveries, Total ALLL - Including Discontinued Operations	45	35
Financing Receivable Allowance For Credit Losses Total ALLL Including Discontinued Operations, Ending Balance	942	1,034
Commercial, financial and agricultural [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations	327	334
Provision	13	(3)
Charge-offs	(14)	(26)
Recoveries	12	11
Balance at end of period - continuing operations	338	316
Commercial real estate: Commercial mortgage [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations	198	272
Provision	3	12
Charge-offs	(13)	(23)
Recoveries	5	2
Balance at end of period - continuing operations	193	263
Commercial Real Estate Construction Financing Receivable [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations	41	63
Provision	(13)	3
Charge-offs	(1)	(11)
Recoveries	8	1
Balance at end of period - continuing operations	35	56
Commercial lease financing [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations	55	78
Provision	9	(10)
Charge-offs	(6)	(4)
Recoveries	4	4
Balance at end of period - continuing operations	62	68
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations	621	747
Provision	12	2
Charge-offs	(34)	(64)
Recoveries	29	18
Balance at end of period - continuing operations	628	703
Real estate - residential mortgage [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations	30	37
Provision	10	4
Charge-offs	(6)	(6)
Recoveries		1
Balance at end of period - continuing operations	34	36
Home equity: Key Community Bank [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations	105	103
Provision	17	14
Charge-offs	(18)	(25)
Recoveries	2	2
Balance at end of period - continuing operations	106	94
Home equity: Other [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations	25	29
Provision	(3)	6
Charge-offs	(6)	(8)
Recoveries	2	1
Balance at end of period - continuing operations	18	28
Home equity [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations	130	132
Provision	14	20
Charge-offs	(24)	(33)
Recoveries	4	3
Balance at end of period - continuing operations	124	122
Consumer other - Key Community Bank [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations	38	41
Provision	2	5
Charge-offs	(9)	(10)
Recoveries	2	1
Balance at end of period - continuing operations	33	37
Credit cards [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations	26
Provision	14
Charge-offs	(8)
Recoveries
Balance at end of period - continuing operations	32
Consumer Marine [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations	39	46
Provision	2	9
Charge-offs	(8)	(17)
Recoveries	5	7
Balance at end of period - continuing operations	38	45
Consumer Others [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations	4	1
Provision		1
Charge-offs	(1)	(2)
Recoveries	1	1
Balance at end of period - continuing operations	4	1
Consumer Other - Key Corporate Bank [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations	43	47
Provision	2	10
Charge-offs	(9)	(19)
Recoveries	6	8
Balance at end of period - continuing operations	42	46
Consumer loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations	267	257
Provision	42	39
Charge-offs	(56)	(68)
Recoveries	12	13
Balance at end of period - continuing operations	$ 265	$ 241