Retirement Benefits (Schedule of Plan Contributions) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Postretirement benefits contributions	$ 323		$ 463		$ 262
Consumers Energy Company [Member]
Postretirement benefits contributions	315		447		254
Other Postretirement Benefit Plans, Defined Benefit [Member]
Postretirement benefits contributions	67		71
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year	65
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	60.00%
Defined Benefit Plan, Target Allocation Percentage of Assets, Debt Securities	40.00%
Other Postretirement Benefit Plans, Defined Benefit [Member] | Consumers Energy Company [Member]
Postretirement benefits contributions	66		70
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year	64
Pension Plans, Defined Benefit [Member]
Postretirement benefits contributions	250	[1]	375	[1]
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	50.00%
Defined Benefit Plan, Target Allocation Percentage of Assets, Debt Securities	30.00%
Defined Benefit Plan Planned Target Allocation Percentage Of Assets, Alternative Investments	20.00%
Pension Plans, Defined Benefit [Member] | Consumers Energy Company [Member]
Postretirement benefits contributions	245	[1]	366	[1]
VEBA Trust [Member] | Other Postretirement Benefit Plans, Defined Benefit [Member]
Postretirement benefits contributions	48	[2]	57	[2]
VEBA Trust [Member] | Other Postretirement Benefit Plans, Defined Benefit [Member] | Consumers Energy Company [Member]
Postretirement benefits contributions	47		57
401 (h) Component [Member] | Other Postretirement Benefit Plans, Defined Benefit [Member]
Postretirement benefits contributions	19	[2]	14	[2]
401 (h) Component [Member] | Other Postretirement Benefit Plans, Defined Benefit [Member] | Consumers Energy Company [Member]
Postretirement benefits contributions	$ 19		$ 13

[1] CMS Energy, including Consumers, does not plan to contribute to the Pension Plan in 2012.

[2] CMS Energy, including Consumers, plans to contribute $65 million to the OPEB plan in 2012 and Consumers plans to contribute $64 million to the OPEB plan in 2012.