Retirement Benefits (Schedule Of SERP Trust Assets, ABO And Contributions) (Details) (DB SERP [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
ABO	$ 122	$ 145
Contributions	16
Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
ABO	82	99
Contributions	13
DB SERP Trust Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Trust assets	136	131
DB SERP Trust Assets [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Trust assets	$ 96	$ 93