Asset Quality - Changes in Allowance for Loan and Lease Losses by Loan Category (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations	$ 893	$ 944	$ 888	$ 1,004
Provision			82	62
Charge-offs	(74)	(131)	(164)	(263)
Recoveries	29	54	70	85
Balance at end of period - continuing operations	876	888	876	888
Discontinued Operations, Beginning Balance			55	104
Provision, Discontinued Operations			5	6
Charge-offs, Discontinued Operations			(28)	(39)
Recoveries, Discontinued Operations			9	8
Discontinued Operations, Ending Balance	41	79	41	79
Financing Receivable Allowance For Credit Losses Total ALLL Including Discontinued Operations, Beginning Balance			943	1,108
Provisions, Total ALLL - Including Discontinued Operations			87	68
Charge-offs, Total ALLL - Including Discontinued Operations			(192)	(302)
Recoveries, Total ALLL - Including Discontinued Operations			79	93
Financing Receivable Allowance For Credit Losses Total ALLL Including Discontinued Operations, Ending Balance	917	967	917	967
Commercial, Financial and Agricultural [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations			327	334
Provision			35	(12)
Charge-offs			(29)	(49)
Recoveries			19	31
Balance at end of period - continuing operations	352	304	352	304
Commercial Real Estate: Commercial Mortgage [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations			198	272
Provision			(10)	8
Charge-offs			(16)	(46)
Recoveries			10	16
Balance at end of period - continuing operations	182	250	182	250
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)	6
Charge-offs			(2)	(16)
Recoveries			8	2
Balance at end of period - continuing operations	34	55	34	55
Commercial Lease Financing [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations			55	78
Provision			6
Charge-offs			(8)	(20)
Recoveries			8	10
Balance at end of period - continuing operations	61	68	61	68
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations			621	747
Provision			18	2
Charge-offs			(55)	(131)
Recoveries			45	59
Balance at end of period - continuing operations	629	677	629	677
Real Estate - Residential Mortgage [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations			30	37
Provision			13
Charge-offs			(10)	(13)
Recoveries				2
Balance at end of period - continuing operations	33	26	33	26
Home Equity: Key Community Bank [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations			105	103
Provision			19	21
Charge-offs			(36)	(48)
Recoveries			6	4
Balance at end of period - continuing operations	94	80	94	80
Home Equity: Other [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations			25	29
Provision				9
Charge-offs			(12)	(17)
Recoveries			3	3
Balance at end of period - continuing operations	16	24	16	24
Home Equity [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations			130	132
Provision			19	30
Charge-offs			(48)	(65)
Recoveries			9	7
Balance at end of period - continuing operations	110	104	110	104
Consumer Other - Key Community Bank [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations			38	41
Provision			7	10
Charge-offs			(16)	(20)
Recoveries			4	3
Balance at end of period - continuing operations	33	34	33	34
Credit Cards [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations			26
Provision			21
Charge-offs			(16)
Recoveries			2
Balance at end of period - continuing operations	33		33
Consumer Marine [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations			39	46
Provision			4	15
Charge-offs			(17)	(30)
Recoveries			9	13
Balance at end of period - continuing operations	35	44	35	44
Consumer Others [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations			4	1
Provision				5
Charge-offs			(2)	(4)
Recoveries			1	1
Balance at end of period - continuing operations	3	3	3	3
Consumer Other - Key Corporate Bank [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations			43	47
Provision			4	20
Charge-offs			(19)	(34)
Recoveries			10	14
Balance at end of period - continuing operations	38	47	38	47
Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations			267	257
Provision			64	60
Charge-offs			(109)	(132)
Recoveries			25	26
Balance at end of period - continuing operations	$ 247	$ 211	$ 247	$ 211