New Accounting Standards (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Unamortized debt issuance costs	$ 40		$ 41
Income Tax Benefit	74	$ 100
New Accounting Pronouncement, Early Adoption, Effect [Member]
Income Tax Benefit	6
Retained Earnings (Accumulated Deficit) [Member]
Cumulative effect of change in accounting principle	33
Consumers Energy Company [Member]
Unamortized debt issuance costs	22		$ 23
Income Tax Benefit	82	$ 110
Consumers Energy Company [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member]
Income Tax Benefit	$ 6