Retirement Benefits (Schedule Of Net Benefit Costs) (Details) - USD ($)		3 Months Ended		9 Months Ended
	Aug. 31, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
DB Pension Plans
Net periodic cost (credit)
Service cost		$ 12,000,000	$ 11,000,000	$ 37,000,000	$ 31,000,000
Interest cost		20,000,000	24,000,000	61,000,000	73,000,000
Expected return on plan assets		(47,000,000)	(40,000,000)	(143,000,000)	(121,000,000)
Settlement loss	$ 36,000,000	1,000,000	0	1,000,000	0
Amortization of:
Net loss		23,000,000	12,000,000	67,000,000	36,000,000
Prior service cost (credit)		0	0	1,000,000	1,000,000
Net periodic cost (credit)		9,000,000	7,000,000	24,000,000	20,000,000
DB Pension Plans | Consumers Energy Company
Net periodic cost (credit)
Service cost		12,000,000	10,000,000	36,000,000	30,000,000
Interest cost		20,000,000	23,000,000	59,000,000	69,000,000
Expected return on plan assets		(45,000,000)	(38,000,000)	(136,000,000)	(114,000,000)
Amortization of:
Net loss		22,000,000	12,000,000	64,000,000	35,000,000
Prior service cost (credit)		0	0	1,000,000	1,000,000
Net periodic cost (credit)		9,000,000	7,000,000	24,000,000	21,000,000
OPEB Plan
Net periodic cost (credit)
Service cost		4,000,000	3,000,000	12,000,000	10,000,000
Interest cost		8,000,000	11,000,000	25,000,000	31,000,000
Expected return on plan assets		(25,000,000)	(22,000,000)	(75,000,000)	(66,000,000)
Settlement loss		0	0	0	0
Amortization of:
Net loss		4,000,000	7,000,000	11,000,000	20,000,000
Prior service cost (credit)		(14,000,000)	(16,000,000)	(42,000,000)	(47,000,000)
Net periodic cost (credit)		(23,000,000)	(17,000,000)	(69,000,000)	(52,000,000)
OPEB Plan | Consumers Energy Company
Net periodic cost (credit)
Service cost		3,000,000	3,000,000	11,000,000	10,000,000
Interest cost		8,000,000	10,000,000	24,000,000	30,000,000
Expected return on plan assets		(23,000,000)	(21,000,000)	(70,000,000)	(62,000,000)
Amortization of:
Net loss		4,000,000	7,000,000	11,000,000	20,000,000
Prior service cost (credit)		(13,000,000)	(15,000,000)	(40,000,000)	(46,000,000)
Net periodic cost (credit)		$ (21,000,000)	$ (16,000,000)	$ (64,000,000)	$ (48,000,000)