Plant, Property, and Equipment (Public Utilities, Allowance for Funds Used During Construction, Schedule of Composite Rate Table) (Details) - Consumers Energy Company	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Electric Utility
Property, Plant and Equipment [Line Items]
AFUDC Capitalization rate	6.90%	6.40%	6.90%
Gas Utility
Property, Plant and Equipment [Line Items]
AFUDC Capitalization rate	5.70%	5.80%	5.90%

Effective rate, including composite rate, of cost of financing additions to qualifying regulated assets, commonly called allowance for funds used during construction.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 835
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6501662&loc=d3e56162-110433

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 835
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6501569&loc=d3e55921-110430

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration