Retirement Benefits (Schedule Of Plan Contributions) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits contributions	$ 108	$ 262	$ 32
Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits contributions	98	243	29
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
DB Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits contributions	100	225
DB Pension Plan [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits contributions	$ 93	$ 209
Equity Securities [Member] | Postretirement Health Trusts [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	50.00%
Equity Securities [Member] | Postretirement Life Trusts [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	42.00%
Equity Securities [Member] | DB Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	53.00%
Fixed Income Funds [Member] | Postretirement Health Trusts [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	30.00%
Fixed Income Funds [Member] | Postretirement Life Trusts [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	28.00%
Fixed Income Funds [Member] | DB Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	32.00%
Alternative Strategy Investments [Member] | Postretirement Health Trusts [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	20.00%
Alternative Strategy Investments [Member] | Postretirement Life Trusts [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	30.00%
Alternative Strategy Investments [Member] | DB Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	15.00%