Financings And Capitalization (Major Long-Term Debt Transactions) (Details) - USD ($)		1 Months Ended	9 Months Ended
		Nov. 30, 2017	Sep. 30, 2017
Debt Instrument [Line Items]
Principal Balance			$ 885,000,000
Debt retirement, principal			430,000,000
CMS Energy [Member]
Debt Instrument [Line Items]
Principal Balance			350,000,000
Consumers Energy Company [Member]
Debt Instrument [Line Items]
Principal Balance			535,000,000
Debt retirement, principal			430,000,000
Senior Notes 3.450% Due August 2027 [Member] | CMS Energy [Member]
Debt Instrument [Line Items]
Principal Balance			$ 350,000,000
Interest rate			3.45%
Debt issuance date			February 2017
Maturity date			August 2027
FMB's 3.950% Due July 2047 [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Principal Balance			$ 350,000,000
Interest rate			3.95%
Debt issuance date			February 2017
Maturity date			July 2047
FMB's 3.180% Due September 2032 [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Principal Balance	[1]		$ 40,000,000
Interest rate	[1]		3.18%
Debt issuance date	[1]		September 2017
Maturity date	[1]		September 2032
FMB's 3.520% Due September 2037 [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Principal Balance	[1]		$ 125,000,000
Interest rate	[1]		3.52%
Debt issuance date	[1]		September 2017
Maturity date	[1]		September 2037
FMB's 3.860% Due September 2052 [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Principal Balance	[1]		$ 20,000,000
Interest rate	[1]		3.86%
Debt issuance date	[1]		September 2017
Maturity date	[1]		September 2052
FMB's 5.150% Due February 2017 [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Debt retirement, principal			$ 250,000,000
Interest rate			5.15%
Debt retirement date			February 2017
Maturity date			February 2017
Senior Notes 6.875% Due March 2018 [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Debt retirement, principal			$ 180,000,000
Interest rate			6.875%
Debt issuance date			September 2017
Maturity date			March 2018
Scenario, Forecast [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Principal Balance		$ 300,000,000
Scenario, Forecast [Member] | FMB's 3.180% Due September 2032 [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Principal Balance		$ 60,000,000
Interest rate		3.18%
Maturity date		2032
Scenario, Forecast [Member] | FMB's 3.520% Due September 2037 [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Principal Balance		$ 210,000,000
Interest rate		3.52%
Maturity date		2037
Scenario, Forecast [Member] | FMB's 3.860% Due September 2052 [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Principal Balance		$ 30,000,000
Interest rate		3.86%
Maturity date		2052

[1] These first mortgage bonds were issued in a September private placement under a bond purchase agreement executed in August. Under the agreement, Consumers will issue an additional $300 million of first mortgage bonds in a second private placement in November, consisting of $60 million of 3.18-percent first mortgage bonds due 2032, $210 million of 3.52-percent first mortgage bonds due 2037, and $30 million of 3.86-percent first mortgage bonds due 2052.