Retirement Benefits (Schedule Of Net Periodic Benefit Cost Not yet Recognized) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Consumers Energy Company
Regulatory assets (liabilities)
Total regulatory assets	$ 1,780	$ 1,784
Regulatory Liabilities	(3,836)	(3,795)
DB Pension Plans and DB SERP
Regulatory assets (liabilities)
Net loss	978	1,017
Prior service cost (credit)	9	11
Total regulatory assets	987	1,028
AOCI
Net loss (gain)	90	97
Prior service cost (credit)	0	1
Total amounts recognized in regulatory assets (liabilities) and AOCI	1,077	1,126
DB Pension Plans and DB SERP | Consumers Energy Company
Regulatory assets (liabilities)
Net loss	978	1,017
Prior service cost (credit)	9	11
Total regulatory assets	987	1,028
AOCI
Net loss (gain)	27	36
Total amounts recognized in regulatory assets (liabilities) and AOCI	1,014	1,064
OPEB Plan
Regulatory assets (liabilities)
Net loss	402	316
Prior service cost (credit)	(361)	(451)
Total regulatory assets	41
Regulatory Liabilities		(135)
AOCI
Net loss (gain)	2	(6)
Prior service cost (credit)	(9)	(12)
Total amounts recognized in regulatory assets (liabilities) and AOCI	34	(153)
OPEB Plan | Consumers Energy Company
Regulatory assets (liabilities)
Net loss	402	316
Prior service cost (credit)	(361)	(451)
Total regulatory assets	41
Regulatory Liabilities		(135)
AOCI
Net loss (gain)	0	0
Total amounts recognized in regulatory assets (liabilities) and AOCI	$ 41	$ (135)