Retirement Benefits (Schedule Of Plan Contributions) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits contributions	$ 32		$ 229		$ 72
Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits contributions	29		222		68
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits contributions	25	[1]	72	[1]
Estimated future employer contributions	29
OPEB [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits contributions	25	[1]	71	[1]
Estimated future employer contributions	29
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits contributions			150	[2]
Pension Plan [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits contributions			147	[2]
VEBA Trust [Member] | OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits contributions	16		55
VEBA Trust [Member] | OPEB [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits contributions	16		55
401 (h) Component [Member] | OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits contributions	9		17
401 (h) Component [Member] | OPEB [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits contributions	$ 9		$ 16
Equity Securities [Member] | OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	50.00%		50.00%
Equity Securities [Member] | OPEB [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	50.00%		50.00%
Equity Securities [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	50.00%		50.00%		50.00%
Equity Securities [Member] | Pension Plan [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	50.00%		50.00%		50.00%
Fixed Income Funds [Member] | OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	25.00%		20.00%
Fixed Income Funds [Member] | OPEB [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	25.00%		20.00%
Fixed Income Funds [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	30.00%		30.00%		30.00%
Fixed Income Funds [Member] | Pension Plan [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	30.00%		30.00%		30.00%
Alternative Strategy Investments [Member] | OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	25.00%		30.00%
Alternative Strategy Investments [Member] | OPEB [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	25.00%		30.00%
Alternative Strategy Investments [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	20.00%		20.00%		20.00%
Alternative Strategy Investments [Member] | Pension Plan [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	20.00%		20.00%		20.00%

[1] CMS Energy, including Consumers, plans to contribute $29 million to the OPEB Plan in 2015, of which Consumers plans to contribute $29 million.

[2] Neither CMS Energy nor Consumers plans to contribute to the DB Pension Plan in 2015.