Retirement Benefits (Tables)

9 Months Ended

Sep. 30, 2017

Defined Benefit Plan Disclosure [Line Items]

Schedule Of Net Benefit Costs

In Millions
	DB Pension Plan												OPEB Plan
	Three Months Ended						Nine Months Ended						Three Months Ended						Nine Months Ended
September 30	2017			2016			2017			2016			2017			2016			2017			2016
CMS Energy, including Consumers
Net periodic cost (credit)
Service cost		$	12		$	10		$	34		$	31		$	5		$	5		$	15		$	14
Interest cost			23			21			67			64			13			12			39			35
Expected return on plan assets			(39)			(36)			(115)			(110)			(22)			(22)			(67)			(65)
Amortization of:
Net loss			20			17			60			52			7			5			23			16
Prior service cost (credit)			1			1			3			3			(8)			(10)			(26)			(31)
Net periodic cost (credit)		$	17		$	13		$	49		$	40		$	(5)		$	(10)		$	(16)		$	(31)
Consumers
Net periodic cost (credit)
Service cost		$	11		$	11		$	33		$	31		$	5		$	4		$	14		$	13
Interest cost			22			20			65			62			12			12			38			34
Expected return on plan assets			(38)			(35)			(112)			(107)			(21)			(20)			(63)			(60)
Amortization of:
Net loss			19			16			58			50			8			5			24			16
Prior service cost (credit)			1			1			3			3			(8)			(10)			(25)			(30)
Net periodic cost (credit)		$	15		$	13		$	47		$	39		$	(4)		$	(9)		$	(12)		$	(27)

Consumers Energy Company [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule Of Net Benefit Costs

In Millions
	DB Pension Plan												OPEB Plan
	Three Months Ended						Nine Months Ended						Three Months Ended						Nine Months Ended
September 30	2017			2016			2017			2016			2017			2016			2017			2016
CMS Energy, including Consumers
Net periodic cost (credit)
Service cost		$	12		$	10		$	34		$	31		$	5		$	5		$	15		$	14
Interest cost			23			21			67			64			13			12			39			35
Expected return on plan assets			(39)			(36)			(115)			(110)			(22)			(22)			(67)			(65)
Amortization of:
Net loss			20			17			60			52			7			5			23			16
Prior service cost (credit)			1			1			3			3			(8)			(10)			(26)			(31)
Net periodic cost (credit)		$	17		$	13		$	49		$	40		$	(5)		$	(10)		$	(16)		$	(31)
Consumers
Net periodic cost (credit)
Service cost		$	11		$	11		$	33		$	31		$	5		$	4		$	14		$	13
Interest cost			22			20			65			62			12			12			38			34
Expected return on plan assets			(38)			(35)			(112)			(107)			(21)			(20)			(63)			(60)
Amortization of:
Net loss			19			16			58			50			8			5			24			16
Prior service cost (credit)			1			1			3			3			(8)			(10)			(25)			(30)
Net periodic cost (credit)		$	15		$	13		$	47		$	39		$	(4)		$	(9)		$	(12)		$	(27)