Amount of expense (reversal of expense) for expected credit loss on accounts receivable.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(5))
-URI http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227

Name:	us-gaap_ProvisionForDoubtfulAccounts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Revenue (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
Revenue (Narrative) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Disaggregation of Revenue [Line Items]
Unbilled receivables	$ 369		$ 437
Consumers Energy Company
Disaggregation of Revenue [Line Items]
Unbilled receivables	369		$ 437
Accounts Receivable
Disaggregation of Revenue [Line Items]
Bad debt expense	6	$ 5
Accounts Receivable \| Consumers Energy Company
Disaggregation of Revenue [Line Items]
Bad debt expense	$ 6	$ 5