Financings and Capitalization (Preferred Stock of Subsidiary) (Details) - USD ($) $ / shares in Units, $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Par value of Preferred Stock	$ 0.01
Shares of Preferred Stock authorized	10,000,000
Consumers Energy Company [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Preferred stock Value	$ 37	$ 37
Preferred Stock $4.50 Series [Member] | Consumers Energy Company [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Par value of Preferred Stock	$ 100	$ 100
Shares of Preferred Stock authorized	7,500,000	7,500,000
Optional Redemption Price	$ 110.00	$ 110.00
Number of Shares	373,148	373,148
Preferred stock Value	$ 37	$ 37