Accumulated Other Comprehensive Income - Reclassifications Out of AOCI (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Corporate services income	$ 43key_BankingServicesIncome	$ 42key_BankingServicesIncome
Interest income - Loans	523	519
Interest expense - Long term debt	(37)us-gaap_InterestExpenseLongTermDebt	(32)us-gaap_InterestExpenseLongTermDebt
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	304	330
Income taxes	(74)us-gaap_IncomeTaxExpenseBenefit	(92)us-gaap_IncomeTaxExpenseBenefit
Income (loss) from continuing operations	230	238
Personnel expense	(389)us-gaap_LaborAndRelatedExpense	(388)us-gaap_LaborAndRelatedExpense
Unrealized Gains (Losses) on Derivative Financial Instruments [Member] \| Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	21	14
Income taxes	8	6
Income (loss) from continuing operations	13	8
Unrealized Gains (Losses) on Derivative Financial Instruments [Member] \| Reclassification out of Accumulated Other Comprehensive Income [Member] \| Interest Rate [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income - Loans	22	15
Interest expense - Long term debt	(1)	(1)
Foreign Currency Translation Adjustment [Member] \| Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Corporate services income		3
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES		3
Income taxes		1
Income (loss) from continuing operations		2
Net Pension and Postretirement Benefit Costs [Member] \| Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	(4)	(4)
Income taxes	(1)	(2)
Income (loss) from continuing operations	(3)	(2)
Net Pension and Postretirement Benefit Costs [Member] \| Reclassification out of Accumulated Other Comprehensive Income [Member] \| Amortization of Losses [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Personnel expense	$ (4)	$ (4)

Banking services income.

No definition available.

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- Definition

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

+ References

+ Details

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 810

-SubTopic 10

-Section 45

-Paragraph 19

-URI http://asc.fasb.org/extlink&oid=7656940&loc=SL4569616-111683

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-08.(h))

-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 08

-Paragraph h

-Article 4

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Income Tax Expense (or Benefit)

-URI http://asc.fasb.org/extlink&oid=6515339

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 9

-Subparagraph (a),(b)

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32639-109319

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-04.1)

-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 1

-Article 9

+ Details

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Balance Type:	credit
Period Type:	duration

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 8

-Article 9

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-04.8)

-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.4)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

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