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=119407570&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=116634182&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		9 Months Ended
Revenue (Narrative) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Uncollectable expense	$ 9	$ 8	$ 21	$ 22
Consumers Energy Company
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Unbilled receivables	$ 249		$ 249		$ 409