Asset Quality - Changes in Allowance for Loan and Lease Losses by Loan Category (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations	$ 876	$ 888	$ 888	$ 1,004
Provision			111
Charge-offs	(78)	(141)	(242)	(404)
Recoveries	41	32	111	117
Balance at end of period - continuing operations	868	888	868	888
Discontinued Operations, Beginning Balance			55	104
Provision, Discontinued Operations			11	4
Charge-offs, Discontinued Operations			(42)	(56)
Recoveries, Discontinued Operations			14	13
Discontinued Operations, Ending Balance	38	65	38	65
Financing Receivable Allowance For Credit Losses Total ALLL Including Discontinued Operations, Beginning Balance			943	1,108
Provisions, Total ALLL - Including Discontinued Operations			122	175
Charge-offs, Total ALLL - Including Discontinued Operations			(284)	(460)
Recoveries, Total ALLL - Including Discontinued Operations			125	130
Financing Receivable Allowance For Credit Losses Total ALLL Including Discontinued Operations, Ending Balance	906	953	906	953
Commercial, Financial and Agricultural [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations			327	334
Provision			57	9
Charge-offs			(44)	(65)
Recoveries			30	40
Balance at end of period - continuing operations	370	318	370	318
Commercial Real Estate: Commercial Mortgage [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations			198	272
Provision			(28)
Charge-offs			(18)	(69)
Recoveries			20	18
Balance at end of period - continuing operations	172	221	172	221
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			(17)
Charge-offs			(2)	(19)
Recoveries			14	3
Balance at end of period - continuing operations	36	47	36	47
Commercial Lease Financing [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations			55	78
Provision			24	(10)
Charge-offs			(25)	(20)
Recoveries			10	18
Balance at end of period - continuing operations	64	66	64	66
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations			621	747
Provision			36	(1)
Charge-offs			(89)	(173)
Recoveries			74	79
Balance at end of period - continuing operations	642	652	642	652
Real Estate - Residential Mortgage [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations			30	37
Provision			17	5
Charge-offs			(13)	(19)
Recoveries			1	2
Balance at end of period - continuing operations	35	25	35	25
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	92
Charge-offs			(50)	(113)
Recoveries			8	7
Balance at end of period - continuing operations	82	89	82	89
Home Equity: Other [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations			25	29
Provision				14
Charge-offs			(16)	(23)
Recoveries			5	4
Balance at end of period - continuing operations	14	24	14	24
Home Equity [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations			130	132
Provision			19	106
Charge-offs			(66)	(136)
Recoveries			13	11
Balance at end of period - continuing operations	96	113	96	113
Consumer Other - Key Community Bank [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations			38	41
Provision			8	15
Charge-offs			(24)	(29)
Recoveries			5	5
Balance at end of period - continuing operations	27	32	27	32
Credit Cards [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations			26
Provision			30	27
Charge-offs			(25)	(2)
Recoveries			3
Balance at end of period - continuing operations	34	25	34	25
Consumer Marine [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations			39	46
Provision			1	14
Charge-offs			(22)	(41)
Recoveries			13	18
Balance at end of period - continuing operations	31	37	31	37
Consumer Others [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations			4	1
Provision				5
Charge-offs			(3)	(4)
Recoveries			2	2
Balance at end of period - continuing operations	3	4	3	4
Consumer Other - Key Corporate Bank [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations			43	47
Provision			1	19
Charge-offs			(25)	(45)
Recoveries			15	20
Balance at end of period - continuing operations	34	41	34	41
Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period - continuing operations			267	257
Provision			75	172
Charge-offs			(153)	(231)
Recoveries			37	38
Balance at end of period - continuing operations	$ 226	$ 236	$ 226	$ 236