New Accounting Standards (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Unamortized debt issuance costs	$ 47	$ 45
Debt retirement premium payments	22	18
Retained Earnings (Accumulated Deficit) [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of change in accounting principle		33
CMS Energy [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt retirement premium payments	18	18
Consumers Energy Company [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Unamortized debt issuance costs	28	$ 25
Debt retirement premium payments	4
Consumers Energy Company [Member] | Accounting Standards Update 2016-01 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Available for sale - Unrealized Gains	$ 19