Retirement Benefits (Narrative) (Details) (OPEB [Member], USD $) In Millions, unless otherwise specified	9 Months Ended
Sep. 30, 2014
Defined Benefit Plan Disclosure [Line Items]
Plan contributions, remainder of fiscal year	$ 25
Estimated future employer contributions	29
Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan contributions, remainder of fiscal year	25
Estimated future employer contributions	$ 29

Amount of employer's best estimate of contributions expected to be paid to the plan during the next fiscal year beginning after the date of the latest statement of financial position.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (g)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

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