COMMONLY OWNED FACILITIES (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010
Commonly Owned Facilities
Proportionate ownership interest (as a percent)	12.00%
Distance of Iatan Generating Facility from Kansas city (in miles)	35
Ownership interest in the site (as a percent)	3.00%
EDE
Commonly Owned Facilities
Ownership interest in certain common facilities (as a percent)	12.00%
Iatan
Commonly Owned Facilities
Proportionate ownership interest (as a percent)	12.00%
Amounts included in property, plant and equipment
Cost of ownership in plant in service	$ 362.6	$ 353.9
Accumulated Depreciation	39.6	34.1
Expenditures	31.3	18.2
Iatan \| EDE
Commonly Owned Facilities
Proportionate ownership interest (as a percent)	12.00%
Iatan1 \| KCP&L
Commonly Owned Facilities
Proportionate ownership interest (as a percent)	70.00%
Iatan1 \| KCP&L Greater Missouri Operations Co.
Commonly Owned Facilities
Proportionate ownership interest (as a percent)	18.00%
Iatan2 \| EDE
Amounts included in property, plant and equipment
Addition to plant in service		212.2
Addition to plant in service for common property expenditures		2.9
Iatan2 \| KCP&L
Commonly Owned Facilities
Proportionate ownership interest (as a percent)	54.00%
Iatan2 \| KCP&L Greater Missouri Operations Co.
Commonly Owned Facilities
Proportionate ownership interest (as a percent)	18.00%
State Line Combined Cycle Unit
Amounts included in property, plant and equipment
Cost of ownership in plant in service	162.1	164.1
Accumulated Depreciation	49.4	44.9
Expenditures	57.0	59.6
Power capacity (in megawatts)	50000.00%
State Line Combined Cycle Unit \| EDE
Commonly Owned Facilities
Percentage share in available capacity	60.00%
Amounts included in property, plant and equipment
Percentage share in operating costs	60.00%
Plum point
Amounts included in property, plant and equipment
Cost of ownership in plant in service	110.1	110.2
Accumulated Depreciation	2.7	0.7
Expenditures	$ 8.5	$ 3.4
Plum point \| EDE
Commonly Owned Facilities
Proportionate ownership interest (as a percent)	7.52%

Represents the total power capacity of a jointly owned utility plant.

No definition available.

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- Definition

Represents the distance of Iatan Generating Facility from Kansas city.

+ References

No definition available.

+ Details

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Namespace Prefix:	ede_
Data Type:	xbrli:integerItemType
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Period Type:	duration

- Definition

Represents the proportionate share of operating costs in a jointly owned utility plant.

+ References

No definition available.

+ Details

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Namespace Prefix:	ede_
Data Type:	num:percentItemType
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Period Type:	duration

- Definition

The share of the available capacity of which the reporting entity is entitled.

+ References

No definition available.

+ Details

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Namespace Prefix:	ede_
Data Type:	num:percentItemType
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- Definition

The expenditure incurred by the reporting entity of a jointly owned utility.

+ References

No definition available.

+ Details

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Namespace Prefix:	ede_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents the addition to jointly owned plant in service.

+ References

No definition available.

+ Details

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Namespace Prefix:	ede_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents the addition to jointly owned plant in service for common property expenditures.

+ References

No definition available.

+ Details

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Namespace Prefix:	ede_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The proportionate ownership interest in common facilities of a jointly owned utility plant.

+ References

No definition available.

+ Details

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Namespace Prefix:	ede_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The proportionate share of interest (percent) in the site at jointly owned facility.

+ References

No definition available.

+ Details

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Namespace Prefix:	ede_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The period end amount owned by the reporting utility of a jointly owned utility plant in service.

+ References

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

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 10

-Section C

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 360

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 10.C)

-URI http://asc.fasb.org/extlink&oid=6500719&loc=d3e659983-123033

+ Details

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Balance Type:	debit
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- Details

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- Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The period end amount of accumulated depreciation in a jointly owned electricity generation plant.

+ References

+ Details

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

- Definition

The proportionate share of interest (percent) in a jointly owned utility plant.

+ References

+ Details

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