Loans and Loans Held for Sale - Loans by Category (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Loans [Line Items]
Commercial, financial and agricultural	$ 27,982	$ 24,963
Commercial real estate:
Commercial mortgage	8,047	7,720
Construction	1,100	1,093
Total commercial real estate loans	9,147	8,813
Commercial lease financing	4,252	4,551
Total commercial loans	41,381	38,327
Residential - Prime Loans:
Real estate - residential mortgage	2,225	2,187
Home equity loans	10,633	10,674
Total residential - prime loans	12,858	12,861
Credit cards	754	722
Consumer other	828	1,098
Total consumer loans	16,000	16,130
Total Loans	57,381	54,457
Other loans [Member]
Residential - Prime Loans:
Home equity loans	267	334
Consumer other	49	70
Marine loans [Member]
Residential - Prime Loans:
Consumer other	779	1,028
Key Community Bank [Member]
Residential - Prime Loans:
Home equity loans	10,366	10,340
Consumer other	$ 1,560	$ 1,449

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Amount before allowance of commercial leases and leveraged lease transactions where the entity is long-term creditor. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes leases covered under loss sharing agreements.

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Amount before allowance of commercial loans and leases receivable includes, but not limited to, commercial and industrial loans, agricultural loans, mortgage loans, promissory notes, interbank and other loans to financial institutions, draws against credit facilities, trade financing, lease financings. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

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Amount before allowance of consumer mortgage. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes subordinated loans such as home equity lines of credit and loans and leases covered under loss sharing agreements.

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Amount before allowance of consumer real estate loans. Includes, but not limited to, construction financing, residential mortgage loans, and home equity lines of credit. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

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Amount before allowance of credit card loans issued to individuals. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

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Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

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Amount before allowance of commercial construction loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans covered under loss sharing agreements.

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Amount before allowance of loans issued to agricultural, commercial and industrial, and financial institutions. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans covered under loss sharing agreements.

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Amount before allowance of mortgage loans on existing land or building. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans covered under loss sharing agreements.

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Amount before allowance of commercial loans issued to businesses to acquire, develop, construct, improve, or refinance land or building. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans covered under loss sharing agreements.

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