Retirement Benefits (Schedule Of Net Periodic Benefit Cost Not yet Recognized) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Pension And DB SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory assets (liabilities), Net loss	$ 625	$ 1,095
Regulatory assets (liabilities), Prior service cost (credit)	9	13
Regulatory assets (liabilities	634	1,108
AOCI, Net loss (gain)	69	98
Total amounts not yet recognized as component of net periodic benefit cost	703	1,206
Pension And DB SERP [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory assets (liabilities), Net loss	625	1,095
Regulatory assets (liabilities), Prior service cost (credit)	9	13
Regulatory assets (liabilities	634	1,108
AOCI, Net loss (gain)	25	38
Total amounts not yet recognized as component of net periodic benefit cost	659	1,146
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory assets (liabilities), Net loss	184	704
Regulatory assets (liabilities), Prior service cost (credit)	(282)	(112)
Regulatory assets (liabilities	(98)	592
AOCI, Net loss (gain)	(26)	(7)
AOCI, Prior service cost (credit)	(10)	(3)
Total amounts not yet recognized as component of net periodic benefit cost	(134)	582
OPEB [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory assets (liabilities), Net loss	184	704
Regulatory assets (liabilities), Prior service cost (credit)	(282)	(112)
Regulatory assets (liabilities	(98)	592
Total amounts not yet recognized as component of net periodic benefit cost	$ (98)	$ 592