Income Taxes (Details) - USD ($) $ in Millions		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016
Income Taxes [Line Items]
U.S. federal income tax rate		35.00%	35.00%
State and local income taxes, net of federal effect		4.70%	3.80%
Accelerated flow-through of regulatory tax benefits	[1]	(4.20%)	(4.60%)
Employee share-based awards		(1.40%)	(1.30%)
Other, net		(1.20%)	(1.50%)
Effective tax rate		32.90%	31.40%
Consumers Energy Company [Member]
Income Taxes [Line Items]
U.S. federal income tax rate		35.00%	35.00%
State and local income taxes, net of federal effect		4.60%	4.60%
Accelerated flow-through of regulatory tax benefits	[1]	(4.00%)	(4.10%)
Employee share-based awards		(1.20%)	(1.20%)
Other, net		(1.60%)	(1.10%)
Effective tax rate		32.80%	33.20%
Reduction of income tax expense		$ 19	$ 19

[1] Since 2014, Consumers has followed a regulatory treatment ordered by the MPSC that accelerates the return of certain income tax benefits to customers. This change, which also accelerates Consumers' recognition of the income tax benefits, reduced Consumers' income tax expense by $19 million for the six months ended June 30, 2017 and 2016.