Plant, Property, and Equipment (Jointly Owned Regulated Utility Facilities) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014
Campbell Unit 3 [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Ownership share	93.30%
Utility plant in service	$ 1,077
Accumulated depreciation	(503)
Construction work-in-progress	358
Net investment	932
Ludington [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Ownership share	51.00%
Utility plant in service	194
Accumulated depreciation	(156)
Construction work-in-progress	175
Net investment	213
Distribution [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Utility plant in service	194
Accumulated depreciation	(63)
Construction work-in-progress	2
Net investment	$ 133

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

Reference 1: 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

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

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 10

-Section C

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- Definition

The total period end amount of plant in service and construction in progress net of accumulated depreciation for the utility's share of jointly owned electricity generation plant.

+ References

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- Definition

The period end amount of construction work in progress at a jointly owned electricity generation plant.

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- Definition

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

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- Definition

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

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