Retirement Benefits (Schedule Of Benefit Obligations In Excess Of Fair Value Of Plan Assets) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at beginning of period	$ 2,354		$ 2,072
Service cost	53		48
Interest cost	94		99
Actuarial (gain) loss	(308)		249
Benefits paid	(120)		(114)
Benefit obligation at end of period	2,073		2,354
Plan assets at fair value at beginning of period	1,727		1,626
Actual return on plan assets	206		215
Company contributions	150
Actual benefits paid	(119)		(114)
Plan assets at fair value at end of period	1,964		1,727
Funded status	(109)	[1]	(627)	[1]
Pension [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Funded status	(86)		(590)
DB SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at beginning of period	144		127
Service cost	1		1
Interest cost	6		6
Actuarial (gain) loss	(12)		16
Benefits paid	(7)		(6)
Benefit obligation at end of period	132		144
Company contributions	7		6
Actual benefits paid	(7)		(6)
Funded status	(132)		(144)
DB SERP [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at beginning of period	100		85
Service cost	1		1
Interest cost	4		4
Actuarial (gain) loss	(8)		13
Benefits paid	(4)		(3)
Benefit obligation at end of period	93		100
Company contributions	4		3
Actual benefits paid	(4)		(3)
Funded status	(93)		(100)
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at beginning of period	1,729	[2]	1,641
Service cost	29		32		27
Interest cost	65		82		77
Plan amendments	(208)	[3]
Actuarial (gain) loss	(440)		25
Benefits paid	(52)	[4]	(51)	[4]
Benefit obligation at end of period	1,123	[2]	1,729	[2]	1,641
Plan assets at fair value at beginning of period	1,047		924
Actual return on plan assets	150		108
Company contributions	72		65
Actual benefits paid	(51)	[4]	(50)	[4]
Plan assets at fair value at end of period	1,218		1,047		924
Funded status	95		(682)
Prescription Drug Benefit, Effect of Subsidy on Net Periodic Postretirement Benefit Cost			20		26
Capitalization Prescription Drug Benefit, Effect of Subsidy on Net Periodic Postretirement Benefit Cost			7		9
Defined Benefit Plan, Gross Prescription Drug Subsidy Receipts Received	5		5		5
OPEB [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at beginning of period	1,670	[2]	1,585
Service cost	28		31		26
Interest cost	63		79		74
Plan amendments	(200)
Actuarial (gain) loss	(424)		24
Benefits paid	(49)	[4]	(49)	[4]
Benefit obligation at end of period	1,088	[2]	1,670	[2]	1,585
Plan assets at fair value at beginning of period	978		861
Actual return on plan assets	141		101
Company contributions	71		64
Actual benefits paid	(49)	[4]	(48)	[4]
Plan assets at fair value at end of period	1,141		978		861
Funded status	53		(692)
Prescription Drug Benefit, Effect of Subsidy on Net Periodic Postretirement Benefit Cost			19		25
Capitalization Prescription Drug Benefit, Effect of Subsidy on Net Periodic Postretirement Benefit Cost			7		9
Defined Benefit Plan, Gross Prescription Drug Subsidy Receipts Received	$ 4		$ 5		$ 5

[1] At December 31, 2013, $86 million of the total funded status of the Pension Plan was attributable to Consumers based on an allocation of expenses. At December 31, 2012, $590 million of the total funded status of the Pension Plan was attributable to Consumers based on an allocation of expenses.

[2] The Medicare Prescription Drug, Improvement, and Modernization Act of 2003 established a prescription drug benefit under Medicare (Medicare Part D) and a federal subsidy, which is tax-exempt, to sponsors of retiree health care benefit plans that provide a benefit that is actuarially equivalent to Medicare Part D. In 2010, the Health Care Acts repealed these tax-exempt deductions for years beginning after December 31, 2012. The Medicare Part D subsidy annualized reduction in net OPEB cost for CMS Energy was $20 million for 2012 and $26 million for 2011. Consumers’ Medicare Part D subsidy annualized reduction in net OPEB costs was $19 million for 2012 and $25 million for 2011. The reduction for CMS Energy and Consumers included $7 million for 2012 and $9 million for 2011 in capitalized OPEB costs.

[3] Plan amendments resulted from changing the Medicare drug program provided through the OPEB Plan from an employer-sponsored prescription drug plan with a retiree drug subsidy to an EGWP to begin on January 1, 2015, and from certain benefit changes to the OPEB Plan, to begin on January 1, 2016.

[4] CMS Energy received payments of $5 million in each of 2013, 2012, and 2011 for the Medicare Part D subsidies. Consumers received payments of $4 million in 2013 and $5 million in each of 2012 and 2011 for the Medicare Part D subsidies. The Medicare Part D subsidy payments are used to pay OPEB Plan benefits.