Income Taxes (Details) - USD ($)
$ in Millions
 9 Months Ended
Sep. 30, 2016
Sep. 30, 2015
Income Taxes [Line Items]    
U.S. federal income tax rate 35.00% 35.00%
State and local income taxes, net of federal effect 4.20% 4.80%
Accelerated flow-through of regulatory tax benefits [1] (4.70%) (4.90%)
Employee share-based awards [2] (0.80%)  
Other, net (1.40%) (1.40%)
Effective tax rate 32.30% 33.50%
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% 4.80%
Accelerated flow-through of regulatory tax benefits [1] (4.00%) (4.20%)
Employee share-based awards [2] (0.70%)  
Other, net (1.20%) (1.50%)
Effective tax rate 33.70% 34.10%
Reduction of income tax expense $ 30 $ 29
[1] Since 2014, Consumers has followed a new 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 $30 million for the nine months ended September 30, 2016 and by $29 million for the nine months ended September 30, 2015.
[2] CMS Energy and Consumers elected to adopt ASU 2016-09, Improvements to Employee Share-Based Payment Accounting, as of January 1, 2016. For further details on the implementation of this standard, see Note 1, New Accounting Standards.