Retirement Benefits (Schedule Of Plan Contributions) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits contributions	$ 262	$ 32	$ 229
Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits contributions	243	29	$ 222
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits contributions	29	25
OPEB [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits contributions	29	25
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits contributions	225
Pension Plan [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits contributions	209
VEBA Trust [Member] | OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits contributions	29	16
VEBA Trust [Member] | OPEB [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits contributions	$ 29	16
401 (h) Component [Member] | OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits contributions		9
401 (h) Component [Member] | OPEB [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits contributions		$ 9
Equity Securities [Member] | OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	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%
Equity Securities [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	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%
Fixed Income Funds [Member] | OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	30.00%
Fixed Income Funds [Member] | OPEB [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	30.00%
Fixed Income Funds [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	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%
Alternative Strategy Investments [Member] | OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	20.00%
Alternative Strategy Investments [Member] | OPEB [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	20.00%
Alternative Strategy Investments [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	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%