Asset Quality (Details 2) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011 Loan
Financing Receivable Modifications [Line Items]
Number of loans	937
Pre-modification Outstanding Recorded Investment	$ 402
Post-modification Outstanding Recorded Investment	276
Nonperforming [Member]
Financing Receivable Modifications [Line Items]
Number of loans	437
Pre-modification Outstanding Recorded Investment	278
Post-modification Outstanding Recorded Investment	191
Prior Year Accruing [Member]
Financing Receivable Modifications [Line Items]
Number of loans	500
Pre-modification Outstanding Recorded Investment	124
Post-modification Outstanding Recorded Investment	85
Commercial, financial and agricultural [Member] | Nonperforming [Member]
Financing Receivable Modifications [Line Items]
Number of loans	13
Pre-modification Outstanding Recorded Investment	71
Post-modification Outstanding Recorded Investment	39
Commercial, financial and agricultural [Member] | Prior Year Accruing [Member]
Financing Receivable Modifications [Line Items]
Number of loans	1
Pre-modification Outstanding Recorded Investment	8
Post-modification Outstanding Recorded Investment	4
Commercial real estate: Commercial Mortgage [Member] | Nonperforming [Member]
Financing Receivable Modifications [Line Items]
Number of loans	15
Pre-modification Outstanding Recorded Investment	120
Post-modification Outstanding Recorded Investment	91
Commercial real estate: Commercial Mortgage [Member] | Prior Year Accruing [Member]
Financing Receivable Modifications [Line Items]
Number of loans	3
Pre-modification Outstanding Recorded Investment	31
Post-modification Outstanding Recorded Investment	22
Commercial real estate: Construction [Member] | Nonperforming [Member]
Financing Receivable Modifications [Line Items]
Number of loans	5
Pre-modification Outstanding Recorded Investment	24
Post-modification Outstanding Recorded Investment	11
Commercial real estate: Construction [Member] | Prior Year Accruing [Member]
Financing Receivable Modifications [Line Items]
Number of loans	3
Pre-modification Outstanding Recorded Investment	39
Post-modification Outstanding Recorded Investment	19
Commercial Real Estate Loans [Member] | Nonperforming [Member]
Financing Receivable Modifications [Line Items]
Number of loans	20
Pre-modification Outstanding Recorded Investment	144
Post-modification Outstanding Recorded Investment	102
Commercial Real Estate Loans [Member] | Prior Year Accruing [Member]
Financing Receivable Modifications [Line Items]
Number of loans	6
Pre-modification Outstanding Recorded Investment	70
Post-modification Outstanding Recorded Investment	41
Commercial Lease Financing [Member] | Nonperforming [Member]
Financing Receivable Modifications [Line Items]
Number of loans	147
Pre-modification Outstanding Recorded Investment	18
Post-modification Outstanding Recorded Investment	7
Commercial Lease Financing [Member] | Prior Year Accruing [Member]
Financing Receivable Modifications [Line Items]
Number of loans	159
Pre-modification Outstanding Recorded Investment	17
Post-modification Outstanding Recorded Investment	13
Commercial Loans [Member] | Nonperforming [Member]
Financing Receivable Modifications [Line Items]
Number of loans	180
Pre-modification Outstanding Recorded Investment	233
Post-modification Outstanding Recorded Investment	148
Commercial Loans [Member] | Prior Year Accruing [Member]
Financing Receivable Modifications [Line Items]
Number of loans	166
Pre-modification Outstanding Recorded Investment	95
Post-modification Outstanding Recorded Investment	58
Real estate - residential mortgage [Member] | Nonperforming [Member]
Financing Receivable Modifications [Line Items]
Number of loans	90
Pre-modification Outstanding Recorded Investment	12
Post-modification Outstanding Recorded Investment	11
Real estate - residential mortgage [Member] | Prior Year Accruing [Member]
Financing Receivable Modifications [Line Items]
Number of loans	54
Pre-modification Outstanding Recorded Investment	6
Post-modification Outstanding Recorded Investment	6
Home Equity Key Community Bank [Member] | Nonperforming [Member]
Financing Receivable Modifications [Line Items]
Number of loans	41
Pre-modification Outstanding Recorded Investment	5
Post-modification Outstanding Recorded Investment	5
Home Equity Key Community Bank [Member] | Prior Year Accruing [Member]
Financing Receivable Modifications [Line Items]
Number of loans	62
Pre-modification Outstanding Recorded Investment	6
Post-modification Outstanding Recorded Investment	6
Home Equity Other [Member] | Nonperforming [Member]
Financing Receivable Modifications [Line Items]
Number of loans	40
Pre-modification Outstanding Recorded Investment	1
Post-modification Outstanding Recorded Investment	1
Home Equity Other [Member] | Prior Year Accruing [Member]
Financing Receivable Modifications [Line Items]
Number of loans	71
Pre-modification Outstanding Recorded Investment	3
Post-modification Outstanding Recorded Investment	2
Home Equity Loans [Member] | Nonperforming [Member]
Financing Receivable Modifications [Line Items]
Number of loans	81
Pre-modification Outstanding Recorded Investment	6
Post-modification Outstanding Recorded Investment	6
Home Equity Loans [Member] | Prior Year Accruing [Member]
Financing Receivable Modifications [Line Items]
Number of loans	133
Pre-modification Outstanding Recorded Investment	9
Post-modification Outstanding Recorded Investment	8
Consumer Other - Key Community Bank [Member] | Nonperforming [Member]
Financing Receivable Modifications [Line Items]
Number of loans	7
Pre-modification Outstanding Recorded Investment	0
Post-modification Outstanding Recorded Investment	0
Consumer Other - Key Community Bank [Member] | Prior Year Accruing [Member]
Financing Receivable Modifications [Line Items]
Number of loans	14
Pre-modification Outstanding Recorded Investment	0
Post-modification Outstanding Recorded Investment	0
Consumer Marine [Member] | Nonperforming [Member]
Financing Receivable Modifications [Line Items]
Number of loans	57
Pre-modification Outstanding Recorded Investment	27
Post-modification Outstanding Recorded Investment	26
Consumer Marine [Member] | Prior Year Accruing [Member]
Financing Receivable Modifications [Line Items]
Number of loans	102
Pre-modification Outstanding Recorded Investment	12
Post-modification Outstanding Recorded Investment	11
Other Consumer [Member] | Nonperforming [Member]
Financing Receivable Modifications [Line Items]
Number of loans	22
Pre-modification Outstanding Recorded Investment	0
Post-modification Outstanding Recorded Investment	0
Other Consumer [Member] | Prior Year Accruing [Member]
Financing Receivable Modifications [Line Items]
Number of loans	31
Pre-modification Outstanding Recorded Investment	2
Post-modification Outstanding Recorded Investment	2
Consumer Other [Member] | Nonperforming [Member]
Financing Receivable Modifications [Line Items]
Number of loans	79
Pre-modification Outstanding Recorded Investment	27
Post-modification Outstanding Recorded Investment	26
Consumer Other [Member] | Prior Year Accruing [Member]
Financing Receivable Modifications [Line Items]
Number of loans	133
Pre-modification Outstanding Recorded Investment	14
Post-modification Outstanding Recorded Investment	13
Consumer Loans [Member] | Nonperforming [Member]
Financing Receivable Modifications [Line Items]
Number of loans	257
Pre-modification Outstanding Recorded Investment	45
Post-modification Outstanding Recorded Investment	43
Consumer Loans [Member] | Prior Year Accruing [Member]
Financing Receivable Modifications [Line Items]
Number of loans	334
Pre-modification Outstanding Recorded Investment	29
Post-modification Outstanding Recorded Investment	$ 27