Variable Interest Entities - Variable Interest Entities Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2013
LIHTC funds [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Carrying Amount of Assets, Consolidated VIEs	$ 50
Variable Interest Entity, Carrying Amount of Liabilities, Consolidated VIEs	63
Variable Interest Entity, Carrying Amount of Assets, Unconsolidated VIEs	113
Variable Interest Entity, Carrying Amount of Liabilities, Unconsolidated VIEs
Maximum Exposure to Loss, Unconsolidated VIEs
Education loan securitization trusts [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Carrying Amount of Assets, Consolidated VIEs	2,358
Variable Interest Entity, Carrying Amount of Liabilities, Consolidated VIEs	2,151
Variable Interest Entity, Carrying Amount of Assets, Unconsolidated VIEs
Variable Interest Entity, Carrying Amount of Liabilities, Unconsolidated VIEs
Maximum Exposure to Loss, Unconsolidated VIEs
LIHTC investments [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Carrying Amount of Assets, Consolidated VIEs
Variable Interest Entity, Carrying Amount of Liabilities, Consolidated VIEs
Variable Interest Entity, Carrying Amount of Assets, Unconsolidated VIEs	793
Variable Interest Entity, Carrying Amount of Liabilities, Unconsolidated VIEs
Maximum Exposure to Loss, Unconsolidated VIEs	$ 448

Maximum exposure to loss unconsolidated vie.

No definition available.

Name:	key_MaximumExposureToLossUnconsolidatedVie
Namespace Prefix:	key_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The carrying amount of the consolidated Variable Interest Entity's assets included in the reporting entity's statement of financial position.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 810

-SubTopic 10

-Section 50

-Paragraph 3

-Subparagraph (bb)

-URI http://asc.fasb.org/extlink&oid=7880789&loc=d3e5710-111685

+ Details

Name:	us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The carrying amount of the consolidated Variable Interest Entity's liabilities included in the reporting entity's statement of financial position.

+ References

+ Details

Name:	us-gaap_VariableInterestEntityConsolidatedCarryingAmountLiabilities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_VariableInterestEntityLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Carrying amount of the assets in the reporting entity's statement of financial position that relate to the reporting entity's variable interest in the Variable Interest Entity (VIE), where the reporting entity is not the VIE's primary beneficiary.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 810

-SubTopic 10

-Section 50

-Paragraph 4

-Subparagraph a

-URI http://asc.fasb.org/extlink&oid=7880789&loc=d3e5728-111685

+ Details

Name:	us-gaap_VariableInterestEntityNonconsolidatedCarryingAmountAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Carrying amount of the liabilities in the reporting entity's statement of financial position that relate to the reporting entity's variable interest in the Variable Interest Entity (VIE), where the reporting entity is not the VIE's primary beneficiary.

+ References

+ Details

Name:	us-gaap_VariableInterestEntityNonconsolidatedCarryingAmountLiabilities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant