Asset Quality (Details 2) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012 Loan
Financing Receivable, Modifications [Line Items]
Number of loans	1,094
Pre-modification Outstanding Recorded Investment	$ 399
Post-modification Outstanding Recorded Investment	274
Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Number of loans	463
Pre-modification Outstanding Recorded Investment	247
Post-modification Outstanding Recorded Investment	163
Prior Year Accruing [Member]
Financing Receivable, Modifications [Line Items]
Number of loans	631
Pre-modification Outstanding Recorded Investment	152
Post-modification Outstanding Recorded Investment	111
Commercial, financial and agricultural [Member] | Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Number of loans	95
Pre-modification Outstanding Recorded Investment	108
Post-modification Outstanding Recorded Investment	59
Commercial, financial and agricultural [Member] | Prior Year Accruing [Member]
Financing Receivable, Modifications [Line Items]
Number of loans	115
Pre-modification Outstanding Recorded Investment	8
Post-modification Outstanding Recorded Investment	6
Commercial real estate: Commercial Mortgage [Member] | Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Number of loans	16
Pre-modification Outstanding Recorded Investment	47
Post-modification Outstanding Recorded Investment	31
Commercial real estate: Commercial Mortgage [Member] | Prior Year Accruing [Member]
Financing Receivable, Modifications [Line Items]
Number of loans	7
Pre-modification Outstanding Recorded Investment	71
Post-modification Outstanding Recorded Investment	48
Commercial real estate: Construction [Member] | Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Number of loans	11
Pre-modification Outstanding Recorded Investment	60
Post-modification Outstanding Recorded Investment	43
Commercial real estate: Construction [Member] | Prior Year Accruing [Member]
Financing Receivable, Modifications [Line Items]
Number of loans	1
Pre-modification Outstanding Recorded Investment	15
Post-modification Outstanding Recorded Investment	1
Commercial Real Estate Loans [Member] | Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Number of loans	27
Pre-modification Outstanding Recorded Investment	107
Post-modification Outstanding Recorded Investment	74
Commercial Real Estate Loans [Member] | Prior Year Accruing [Member]
Financing Receivable, Modifications [Line Items]
Number of loans	8
Pre-modification Outstanding Recorded Investment	86
Post-modification Outstanding Recorded Investment	49
Commercial Loans [Member] | Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Number of loans	122
Pre-modification Outstanding Recorded Investment	215
Post-modification Outstanding Recorded Investment	133
Commercial Loans [Member] | Prior Year Accruing [Member]
Financing Receivable, Modifications [Line Items]
Number of loans	123
Pre-modification Outstanding Recorded Investment	94
Post-modification Outstanding Recorded Investment	55
Real estate - residential mortgage [Member] | Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Number of loans	56
Pre-modification Outstanding Recorded Investment	7
Post-modification Outstanding Recorded Investment	7
Real estate - residential mortgage [Member] | Prior Year Accruing [Member]
Financing Receivable, Modifications [Line Items]
Number of loans	111
Pre-modification Outstanding Recorded Investment	11
Post-modification Outstanding Recorded Investment	11
Home Equity Key Community Bank [Member] | Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Number of loans	50
Pre-modification Outstanding Recorded Investment	4
Post-modification Outstanding Recorded Investment	4
Home Equity Key Community Bank [Member] | Prior Year Accruing [Member]
Financing Receivable, Modifications [Line Items]
Number of loans	88
Pre-modification Outstanding Recorded Investment	7
Post-modification Outstanding Recorded Investment	7
Home Equity Other [Member] | Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Number of loans	74
Pre-modification Outstanding Recorded Investment	2
Post-modification Outstanding Recorded Investment	1
Home Equity Other [Member] | Prior Year Accruing [Member]
Financing Receivable, Modifications [Line Items]
Number of loans	101
Pre-modification Outstanding Recorded Investment	3
Post-modification Outstanding Recorded Investment	3
Home Equity Loans [Member] | Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Number of loans	124
Pre-modification Outstanding Recorded Investment	6
Post-modification Outstanding Recorded Investment	5
Home Equity Loans [Member] | Prior Year Accruing [Member]
Financing Receivable, Modifications [Line Items]
Number of loans	189
Pre-modification Outstanding Recorded Investment	10
Post-modification Outstanding Recorded Investment	10
Consumer other - Key Community Bank [Member] | Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Number of loans	11
Pre-modification Outstanding Recorded Investment	1
Post-modification Outstanding Recorded Investment	1
Consumer other - Key Community Bank [Member] | Prior Year Accruing [Member]
Financing Receivable, Modifications [Line Items]
Number of loans	20
Pre-modification Outstanding Recorded Investment	1
Consumer Marine [Member] | Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Number of loans	139
Pre-modification Outstanding Recorded Investment	17
Post-modification Outstanding Recorded Investment	17
Consumer Marine [Member] | Prior Year Accruing [Member]
Financing Receivable, Modifications [Line Items]
Number of loans	135
Pre-modification Outstanding Recorded Investment	34
Post-modification Outstanding Recorded Investment	33
Other Consumer [Member] | Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Number of loans	11
Pre-modification Outstanding Recorded Investment	1
Other Consumer [Member] | Prior Year Accruing [Member]
Financing Receivable, Modifications [Line Items]
Number of loans	53
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	150
Pre-modification Outstanding Recorded Investment	18
Post-modification Outstanding Recorded Investment	17
Consumer Other [Member] | Prior Year Accruing [Member]
Financing Receivable, Modifications [Line Items]
Number of loans	188
Pre-modification Outstanding Recorded Investment	36
Post-modification Outstanding Recorded Investment	35
Consumer Loans [Member] | Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Number of loans	341
Pre-modification Outstanding Recorded Investment	32
Post-modification Outstanding Recorded Investment	30
Consumer Loans [Member] | Prior Year Accruing [Member]
Financing Receivable, Modifications [Line Items]
Number of loans	508
Pre-modification Outstanding Recorded Investment	58
Post-modification Outstanding Recorded Investment	$ 56