Retirement Benefits (Schedule Of Benefit Obligations In Excess Of Fair Value Of Plan Assets) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
DB Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at beginning of period		$ 2,403	$ 2,547
Service cost		42	49
Interest cost		85	102
Plan amendments			13
Actuarial (gain) loss	[1]	196	(153)
Benefits paid		(164)	(155)
Benefit obligation at end of period		2,562	2,403	$ 2,547
Plan assets at fair value at beginning of period		2,013	1,979
Actual return on plan assets		152	(36)
Company contributions		100	225
Actual benefits paid		(164)	(155)
Plan assets at fair value at end of period		2,101	2,013	1,979
Funded status	[1],[2]	(461)	(390)
DB Pension Plan [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Funded status		(441)	(368)
DB SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at beginning of period		150	156
Service cost			1
Interest cost		5	6
Actuarial (gain) loss		4	(5)
Benefits paid		(8)	(8)
Benefit obligation at end of period		151	150	156
Company contributions		8	8
Actual benefits paid		(8)	(8)
Funded status		(151)	(150)
DB SERP [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at beginning of period		106	111
Service cost			1
Interest cost		4	4
Actuarial (gain) loss	[1]	4	(5)
Benefits paid		(5)	(5)
Benefit obligation at end of period		109	106	111
Company contributions		5	5
Actual benefits paid		(5)	(5)
Funded status		(109)	(106)
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at beginning of period		1,227	1,378
Service cost		18	25	20
Interest cost		46	58	56
Plan amendments			(25)
Actuarial (gain) loss	[1]	171	(152)
Benefits paid		(54)	(57)
Benefit obligation at end of period		1,408	1,227	1,378
Plan assets at fair value at beginning of period		1,208	1,265
Actual return on plan assets		109	(29)
Company contributions			29
Actual benefits paid		(53)	(57)
Plan assets at fair value at end of period		1,264	1,208	1,265
Funded status		(144)	(19)
OPEB [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at beginning of period		1,188	1,336
Service cost		17	25	20
Interest cost		45	56	54
Plan amendments			(24)
Actuarial (gain) loss	[1]	167	(150)
Benefits paid		(52)	(55)
Benefit obligation at end of period		1,365	1,188	1,336
Plan assets at fair value at beginning of period		1,133	1,186
Actual return on plan assets		103	(27)
Company contributions			29
Actual benefits paid		(52)	(55)
Plan assets at fair value at end of period		1,184	1,133	$ 1,186
Funded status		$ (181)	$ (55)

[1] The actuarial loss for 2016 was primarily the result of claims, experience, and lowering the discount rates used in calculating the plans' obligations. The actuarial gain for 2015 was primarily the result of increasing the discount rates used in calculating the plans' obligations.

[2] At December 31, 2016, $441 million of the total funded status of the DB Pension Plan was attributable to Consumers, based on an allocation of expenses. At December 31, 2015, $368 million of the total funded status of the DB Pension Plan was attributable to Consumers, based on an allocation of expenses.