Plant, Property, and Equipment (Schedule of Finite-Lived Intangible Assets by Major Class Table) (Details) - USD ($)		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Public Utility, Property, Plant and Equipment [Line Items]
Finite-Lived Intangible Assets, Gross	[1]	$ 1,158,000,000	$ 1,052,000,000
Finite-Lived Intangible Assets, Accumulated Amortization		561,000,000	444,000,000
Consumers Energy Company [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Finite-Lived Intangible Assets, Gross	[1]	1,143,000,000	1,043,000,000
Finite-Lived Intangible Assets, Accumulated Amortization		555,000,000	440,000,000
Public Utilities, Property Plant and Equipment Additions		1,700,000,000	2,300,000,000
Public Utilities, Property Plant and Equipment Disposals		214,000,000	285,000,000
Software Development Costs [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Finite-Lived Intangible Assets, Gross	[1]	950,000,000	853,000,000
Finite-Lived Intangible Assets, Accumulated Amortization		481,000,000	367,000,000
Software Development Costs [Member] | Consumers Energy Company [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Finite-Lived Intangible Assets, Gross	[1]	937,000,000	845,000,000
Finite-Lived Intangible Assets, Accumulated Amortization		475,000,000	363,000,000
Leasehold Improvements [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Finite-Lived Intangible Assets, Gross	[1],[2]	9,000,000	7,000,000
Finite-Lived Intangible Assets, Accumulated Amortization	[2]	7,000,000	6,000,000
Leasehold Improvements [Member] | Consumers Energy Company [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Finite-Lived Intangible Assets, Gross	[1],[2]	9,000,000	7,000,000
Finite-Lived Intangible Assets, Accumulated Amortization	[2]	7,000,000	6,000,000
Intangible Plant [Member] | Consumers Energy Company [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Property Plant and Equipment Additions		100,000,000	141,000,000
Public Utilities, Property Plant and Equipment Disposals		0	23,000,000
Rights of Way [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Finite-Lived Intangible Assets, Gross	[1]	162,000,000	155,000,000
Finite-Lived Intangible Assets, Accumulated Amortization		50,000,000	48,000,000
Rights of Way [Member] | Consumers Energy Company [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Finite-Lived Intangible Assets, Gross	[1]	162,000,000	155,000,000
Finite-Lived Intangible Assets, Accumulated Amortization		50,000,000	48,000,000
Franchises and Consents [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Finite-Lived Intangible Assets, Gross	[1]	14,000,000	15,000,000
Finite-Lived Intangible Assets, Accumulated Amortization		8,000,000	8,000,000
Franchises and Consents [Member] | Consumers Energy Company [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Finite-Lived Intangible Assets, Gross	[1]	14,000,000	15,000,000
Finite-Lived Intangible Assets, Accumulated Amortization		8,000,000	8,000,000
Other Intangible Assets [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Finite-Lived Intangible Assets, Gross	[1]	23,000,000	22,000,000
Finite-Lived Intangible Assets, Accumulated Amortization		15,000,000	15,000,000
Other Intangible Assets [Member] | Consumers Energy Company [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Finite-Lived Intangible Assets, Gross	[1]	21,000,000	21,000,000
Finite-Lived Intangible Assets, Accumulated Amortization		$ 15,000,000	$ 15,000,000
Minimum [Member] | Software Development Costs [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Finite-Lived Intangible Asset, Useful Life		1 year
Minimum [Member] | Software Development Costs [Member] | Consumers Energy Company [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Finite-Lived Intangible Asset, Useful Life		3 years
Minimum [Member] | Rights of Way [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Finite-Lived Intangible Asset, Useful Life		50 years
Minimum [Member] | Rights of Way [Member] | Consumers Energy Company [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Finite-Lived Intangible Asset, Useful Life		50 years
Minimum [Member] | Franchises and Consents [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Finite-Lived Intangible Asset, Useful Life		5 years
Minimum [Member] | Franchises and Consents [Member] | Consumers Energy Company [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Finite-Lived Intangible Asset, Useful Life		5 years
Maximum [Member] | Software Development Costs [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Finite-Lived Intangible Asset, Useful Life		15 years
Maximum [Member] | Software Development Costs [Member] | Consumers Energy Company [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Finite-Lived Intangible Asset, Useful Life		15 years
Maximum [Member] | Rights of Way [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Finite-Lived Intangible Asset, Useful Life		85 years
Maximum [Member] | Rights of Way [Member] | Consumers Energy Company [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Finite-Lived Intangible Asset, Useful Life		85 years
Maximum [Member] | Franchises and Consents [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Finite-Lived Intangible Asset, Useful Life		30 years
Maximum [Member] | Franchises and Consents [Member] | Consumers Energy Company [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Finite-Lived Intangible Asset, Useful Life		30 years

[1] For the year ended December 31, 2017, Consumers' intangible asset additions were $100 million and there were no retirements. For the year ended December 31, 2016, Consumers' intangible asset additions were $141 million and intangible asset retirements were $23 million.

[2] Leasehold improvements are amortized over the life of the lease, which may change whenever the lease is renewed or extended.