Financings and Capitalization (Preferred Stock of Subsidiary) (Details) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Debt and Equity Securities, FV-NI [Line Items]
Par value of preferred stock (in dollars per share)	$ 0.01
Preferred stock authorized (in shares)	10,000,000
Preferred Stock $4.50 Series | Consumers Energy Company
Debt and Equity Securities, FV-NI [Line Items]
Par value of preferred stock (in dollars per share)	$ 100	$ 100
Optional redemption price (in dollars per share)	$ 110.00	$ 110
Preferred stock authorized (in shares)	7,500,000	7,500,000
Number of shares outstanding (in shares)	373,148	373,148