Contingencies And Commitments (Contingencies And Commitments) (Details) $ in Thousands		1 Months Ended		3 Months Ended		9 Months Ended		12 Months Ended
	Jan. 31, 2019 USD ($)	May 30, 2020 USD ($)	Jan. 31, 2019 USD ($)	Sep. 30, 2020 USD ($) site	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) lawsuit site	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) lawsuit	Mar. 31, 2020 USD ($)
Loss Contingencies [Line Items]
Regulatory assets				$ 2,745,000		$ 2,745,000		$ 2,489,000
Consumers Energy Company
Loss Contingencies [Line Items]
Regulatory assets				2,745,000		2,745,000		$ 2,489,000
Cost of gas sold				33,000	$ 32,000	383,000	$ 537,000
Bay Harbor
Loss Contingencies [Line Items]
Accrual for obligations for environmental remediation				$ 44,000		$ 44,000
Discounted projected costs rate				4.34%		4.34%
Accrual for environmental loss contingencies, inflation rate				1.00%		1.00%
Remaining undiscounted obligation amount				$ 55,000		$ 55,000
Electric Utility | NREPA | Consumers Energy Company
Loss Contingencies [Line Items]
Accrual for obligations for environmental remediation				3,000		3,000
Electric Utility | NREPA | Minimum | Consumers Energy Company
Loss Contingencies [Line Items]
Remediation and other response activity costs				3,000		3,000
Electric Utility | NREPA | Maximum | Consumers Energy Company
Loss Contingencies [Line Items]
Remediation and other response activity costs				4,000		4,000
Electric Utility | CERCLA Liability | Consumers Energy Company
Loss Contingencies [Line Items]
Accrual for obligations for environmental remediation				3,000		3,000
Electric Utility | CERCLA Liability | Minimum | Consumers Energy Company
Loss Contingencies [Line Items]
Remediation and other response activity costs				3,000		3,000
Electric Utility | CERCLA Liability | Maximum | Consumers Energy Company
Loss Contingencies [Line Items]
Remediation and other response activity costs				8,000		8,000
Gas Utility | NREPA | Consumers Energy Company
Loss Contingencies [Line Items]
Accrual for obligations for environmental remediation				1,000		1,000
Gas Utility | NREPA | Maximum | Consumers Energy Company
Loss Contingencies [Line Items]
Remediation and other response activity costs				3,000		3,000
Gas Utility | Manufactured Gas Plant | Consumers Energy Company
Loss Contingencies [Line Items]
Accrual for obligations for environmental remediation				$ 57,000		$ 57,000
Discounted projected costs rate				2.57%		2.57%
Accrual for environmental loss contingencies, inflation rate				2.50%		2.50%
Remaining undiscounted obligation amount				$ 62,000		$ 62,000
Number of former MGPs | site				23		23
Authorized recovery, collection period						10 years
Regulatory assets				$ 122,000		$ 122,000
Equatorial Guinea Tax Claim
Loss Contingencies [Line Items]
Foreign government tax claim on sale						$ 152,000
Class Action Lawsuits
Loss Contingencies [Line Items]
Number of lawsuits | lawsuit						4
Individual Lawsuits
Loss Contingencies [Line Items]
Number of lawsuits | lawsuit						1
Gas Index Price Reporting Litigation
Loss Contingencies [Line Items]
Number of lawsuits | lawsuit								2
Estimated litigation liability								$ 30,000
MCV PPA | Consumers Energy Company
Loss Contingencies [Line Items]
Foreign government tax claim on sale			$ 270,000
Underwater cables Straits of Mackinac | Minimum | Consumers Energy Company
Loss Contingencies [Line Items]
Asset retirement obligation									$ 5,000
Civil Case, Consumers V. MPSC Staff | Consumers Energy Company
Loss Contingencies [Line Items]
Civil penalty settlement		$ 10
Ray Compressor Station | Consumers Energy Company
Loss Contingencies [Line Items]
Cost of gas sold	$ 7,000
Capital expenditures						$ 17,000