Plant, Property, and Equipment (Jointly Owned Regulated Utility Facilities) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012
Campbell Unit 3 [Member]
Jointly Owned Utility Plant, Proportionate Ownership Share	93.30%
Jointly Owned Utility Plant, Gross Ownership Amount of Plant in Service	$ 1,080
Jointly Owned Utility Plant, Ownership Amount of Plant Accumulated Depreciation	(431)
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress	84
Jointly Owned Utility Plant, Net Ownership Amount	733
Ludington [Member]
Jointly Owned Utility Plant, Proportionate Ownership Share	51.00%
Jointly Owned Utility Plant, Gross Ownership Amount of Plant in Service	175
Jointly Owned Utility Plant, Ownership Amount of Plant Accumulated Depreciation	(147)
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress	87
Jointly Owned Utility Plant, Net Ownership Amount	115
Distribution [Member]
Jointly Owned Utility Plant, Gross Ownership Amount of Plant in Service	182
Jointly Owned Utility Plant, Ownership Amount of Plant Accumulated Depreciation	(56)
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress	5
Jointly Owned Utility Plant, Net Ownership Amount	$ 131

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

+ Details

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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.

+ References

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- Definition

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

+ References

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- Definition

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

+ References

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