Jointly-Owned Utility Plant (Detail Textuals)	Dec. 31, 2015 facilities
Jointly-Owned Utility Plant Interests [Line Items]
Number of power plants owned	2
Belle River Unit 1
Jointly-Owned Utility Plant Interests [Line Items]
Ownership interest	63.00%
Belle River Facilities used jointly by Belle River and St. Clair Power Plants
Jointly-Owned Utility Plant Interests [Line Items]
Ownership interest	81.00%
Belle River Unit 2
Jointly-Owned Utility Plant Interests [Line Items]
Ownership interest	75.00%
Belle River
Jointly-Owned Utility Plant Interests [Line Items]
Percent of the total capacity and energy of the plant	19.00%
Ludington Hydroelectric Pumped Storage
Jointly-Owned Utility Plant Interests [Line Items]
Ownership interest	49.00%
Percent of the total capacity and energy of the plant	51.00%