Retirement Benefits (Schedule Of Net Periodic Benefit Cost Not yet Recognized) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Pension And DB SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory assets (liabilities), Net loss	$ 1,012	$ 625
Regulatory assets (liabilities), Prior service cost (credit)	7	9
Regulatory assets (liabilities)	1,019	634
AOCI, Net loss (gain)	99	69
AOCI, Prior service cost (credit)	1
Total amounts not yet recognized as component of net periodic benefit cost	1,119	703
Pension And DB SERP [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory assets (liabilities), Net loss	1,012	625
Regulatory assets (liabilities), Prior service cost (credit)	7	9
Regulatory assets (liabilities)	1,019	634
AOCI, Net loss (gain)	39	25
Total amounts not yet recognized as component of net periodic benefit cost	1,058	659
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory assets (liabilities), Net loss	419	184
Regulatory assets (liabilities), Prior service cost (credit)	(243)	(282)
Regulatory assets (liabilities)	176	(98)
AOCI, Net loss (gain)	(18)	(26)
AOCI, Prior service cost (credit)	(8)	(10)
Total amounts not yet recognized as component of net periodic benefit cost	150	(134)
OPEB [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory assets (liabilities), Net loss	419	184
Regulatory assets (liabilities), Prior service cost (credit)	(243)	(282)
Regulatory assets (liabilities)	176	(98)
Total amounts not yet recognized as component of net periodic benefit cost	$ 176	$ (98)