Contingencies and Commitments (Contingencies And Commitments) (Details) $ in Thousands	1 Months Ended		12 Months Ended
	May 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2020 USD ($) lawsuit site	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jan. 31, 2019 USD ($)
Loss Contingencies [Line Items]
ARO liability incurred			$ 65,000		$ 55,000
Regulatory assets			2,653,000		2,489,000
Consumers Energy Company
Loss Contingencies [Line Items]
ARO liability incurred			46,000		55,000
Regulatory assets			2,653,000		2,489,000
Cost of gas sold			568,000		754,000		$ 819,000
Plant additions			2,000,000		2,000,000
Consumers Energy Company | GCR underrecoveries
Loss Contingencies [Line Items]
Cost of gas sold				$ 500,000		$ 600,000
Bay Harbor
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies			$ 45,000
Discounted projected costs rate			4.34%
Accrual for environmental loss contingencies, inflation rate			1.00%
Remaining undiscounted obligation amount			$ 57,000
CERCLA Liability | Consumers Energy Company
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies			3,000
CERCLA Liability | Minimum | Consumers Energy Company
Loss Contingencies [Line Items]
Remediation and other response activity costs			3,000
CERCLA Liability | Maximum | Consumers Energy Company
Loss Contingencies [Line Items]
Remediation and other response activity costs			8,000
Manufactured Gas Plant | Consumers Energy Company
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies			$ 56,000
Discounted projected costs rate			2.57%
Accrual for environmental loss contingencies, inflation rate			2.50%
Remaining undiscounted obligation amount			$ 61,000
Number of former MGPs | site			23
Regulatory asset collection period			10 years
Electric Utility | NREPA | Consumers Energy Company
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies			$ 2,000
Electric Utility | NREPA | Minimum | Consumers Energy Company
Loss Contingencies [Line Items]
Remediation and other response activity costs			2,000
Electric Utility | NREPA | Maximum | Consumers Energy Company
Loss Contingencies [Line Items]
Remediation and other response activity costs			4,000
Gas Utility | NREPA | Consumers Energy Company
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies			1,000
Gas Utility | NREPA | Maximum | Consumers Energy Company
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies			3,000
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]
Estimated current litigation liability					$ 30,000
MCV PPA | Consumers Energy Company
Loss Contingencies [Line Items]
Remediation and other response activity costs								$ 270,000
Underwater cables Straits of Mackinac | Consumers Energy Company
Loss Contingencies [Line Items]
ARO liability incurred		$ 5,000
Civil Case, Consumers V. MPSC Staff | Consumers Energy Company
Loss Contingencies [Line Items]
Civil penalty	$ 10
Ray Compressor Station | Consumers Energy Company
Loss Contingencies [Line Items]
Plant additions			$ 17,000
Ray Compressor Station | Consumers Energy Company | GCR underrecoveries
Loss Contingencies [Line Items]
Cost of gas sold						$ 7,000