Accumulated Other Comprehensive Income - Reclassifications Out of AOCI (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Corporate services income	$ 178key_BankingServicesIncome	$ 172key_BankingServicesIncome	$ 168key_BankingServicesIncome
Interest income - Loans	2,110	2,151	2,155
Interest expense - Long term debt	(133)us-gaap_InterestExpenseLongTermDebt	(127)us-gaap_InterestExpenseLongTermDebt	(173)us-gaap_InterestExpenseLongTermDebt
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	1,272	1,141	1,073
Income taxes	(326)us-gaap_IncomeTaxExpenseBenefit	(271)us-gaap_IncomeTaxExpenseBenefit	(231)us-gaap_IncomeTaxExpenseBenefit
Income (loss) from continuing operations	946	870	842
Personnel expense	(1,591)us-gaap_LaborAndRelatedExpense	(1,609)us-gaap_LaborAndRelatedExpense	(1,570)us-gaap_LaborAndRelatedExpense
Realized Gain [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other income		1
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES		1
Income (loss) from continuing operations		1
Unrealized Gains (Losses) on Derivative Financial Instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	63	56
Income taxes	23	21
Income (loss) from continuing operations	40	35
Unrealized Gains (Losses) on Derivative Financial Instruments [Member] \| Interest Rate [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest income - Loans	67	67
Interest expense - Long term debt	(4)	(8)
Unrealized Gains (Losses) on Derivative Financial Instruments [Member] \| Foreign Exchange [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other income		(3)
Foreign Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Corporate services income	3	7
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	3	7
Income taxes		3
Income (loss) from continuing operations	3	4
Net Pension and Postretirement Benefit Costs [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	(37)	(45)
Income taxes	(14)	(17)
Income (loss) from continuing operations	(23)	(28)
Net Pension and Postretirement Benefit Costs [Member] \| Amortization of Losses [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Personnel expense	(15)	(19)
Net Pension and Postretirement Benefit Costs [Member] \| Settlement Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Personnel expense	(23)	(27)
Net Pension and Postretirement Benefit Costs [Member] \| Amortization of Prior Service Credit [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Personnel expense	$ 1	$ 1

Banking services income.

No definition available.

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Sum of operating profit and nonoperating income or expense before Income or Loss from equity method investments, income taxes, extraordinary items, and noncontrolling interest.

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This element represents the income or loss from continuing operations attributable to the economic entity which may also be defined as revenue less expenses and taxes from ongoing operations before extraordinary items, and noncontrolling interest.

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-Publisher FASB

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Interest and fee income generated by loans the Entity intends and has the ability to hold for the foreseeable future, or until maturity or payoff, including commercial and consumer loans, whether domestic or foreign, which may consist of: (1) industrial and agricultural; (2) real estate; and (3) real estate construction loans; (4) trade financing; (5) lease financing; (6) home equity lines-of-credit; (7) automobile and other vehicle loans; and (8) credit card and other revolving-type loans. Also includes interest income for leases held by the Entity.

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Aggregate amount of interest paid or due on all long-term debt.

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The aggregate amount of expenditures for salaries, wages, profit sharing and incentive compensation, and other employee benefits, including equity-based compensation, and pension and other postretirement benefit expense.

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Reflects the sum of all other revenue and income recognized by the entity in the period not otherwise specified in the income statement.

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