Contingencies and Commitments (Contingencies And Commitments) (Details) $ in Thousands	1 Months Ended		3 Months Ended		9 Months Ended		32 Months Ended
	Sep. 30, 2020 USD ($)	May 31, 2020 USD ($)	Sep. 30, 2021 USD ($) site MW	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) site MW	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) site MW	Dec. 31, 2020 USD ($)
Loss Contingencies [Line Items]
Regulatory assets			$ 2,588,000		$ 2,588,000		$ 2,588,000	$ 2,653,000
Operating Revenue			1,725,000	$ 1,507,000	5,296,000	$ 4,691,000
Consumers Energy Company
Loss Contingencies [Line Items]
Regulatory assets			2,588,000		2,588,000		2,588,000	$ 2,653,000
Cost of gas sold			53,000	33,000	425,000	383,000
Maintenance and other operating expenses			(390,000)	(266,000)	(1,021,000)	(846,000)
Operating Revenue			1,644,000	$ 1,450,000	5,074,000	$ 4,524,000
Consumers Energy Company | Manufactured Gas Plant
Loss Contingencies [Line Items]
Regulatory assets			114,000		114,000		114,000
Bay Harbor
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies			$ 44,000		$ 44,000		$ 44,000
Discounted projected costs rate			4.34%		4.34%		4.34%
Accrual for environmental loss contingencies, inflation rate			1.00%		1.00%		1.00%
Remaining undiscounted obligation amount			$ 54,000		$ 54,000		$ 54,000
CERCLA Liability | Consumers Energy Company
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies			3,000		3,000		3,000
CERCLA Liability | Minimum | Consumers Energy Company
Loss Contingencies [Line Items]
Remediation and other response activity costs			3,000		3,000		3,000
CERCLA Liability | Maximum | Consumers Energy Company
Loss Contingencies [Line Items]
Remediation and other response activity costs			8,000		8,000		8,000
Manufactured Gas Plant | Consumers Energy Company
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies			$ 57,000		$ 57,000		$ 57,000
Discounted projected costs rate			2.57%		2.57%		2.57%
Accrual for environmental loss contingencies, inflation rate			2.50%		2.50%		2.50%
Remaining undiscounted obligation amount			$ 62,000		$ 62,000		$ 62,000
Number of former MGPs | site			23		23		23
Regulatory asset collection period					10 years
Electric Utility | NREPA | Consumers Energy Company
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies			$ 2,000		$ 2,000		$ 2,000
Electric Utility | NREPA | Minimum | Consumers Energy Company
Loss Contingencies [Line Items]
Remediation and other response activity costs			2,000		2,000		2,000
Electric Utility | NREPA | Maximum | Consumers Energy Company
Loss Contingencies [Line Items]
Remediation and other response activity costs			4,000		4,000		4,000
Gas Utility | NREPA | Consumers Energy Company
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies			1,000		1,000		1,000
Gas Utility | NREPA | Maximum | Consumers Energy Company
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies			3,000		3,000		3,000
Equatorial Guinea Tax Claim
Loss Contingencies [Line Items]
Foreign government tax claim on sale			$ 152,000		$ 152,000		$ 152,000
Civil Case, Consumers V. MPSC Staff | Consumers Energy Company
Loss Contingencies [Line Items]
Civil penalty		$ 10
New Covert Generating Facility | Consumers Energy Company
Loss Contingencies [Line Items]
Nameplate capacity (in MW) | MW			1,176		1,176		1,176
Long-term purchase commitment, amount					$ 810,000
Enterprise Segment Generating Units | Consumers Energy Company
Loss Contingencies [Line Items]
Nameplate capacity (in MW) | MW			1,001		1,001		1,001
Long-term purchase commitment, amount					$ 515,000
Ray Compressor Station | Consumers Energy Company
Loss Contingencies [Line Items]
Plant additions							$ 17,000
Insurance recoveries			$ 10,000		10,000		$ 10,000
Ray Compressor Station | Consumers Energy Company | Insurance Recoveries
Loss Contingencies [Line Items]
Reduction to plant, property and equipment					4,000
Maintenance and other operating expenses					3,000
Operating Revenue					$ 3,000
Ray Compressor Station | Consumers Energy Company | GCR underrecoveries
Loss Contingencies [Line Items]
Cost of gas sold	$ 7,000