Retirement Benefits (Schedule Of Allocation Of Plan Assets) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	$ 1,979	$ 1,964
Pension Plan [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	629	558
Pension Plan [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	1,350	1,406
Pension Plan [Member] | Cash and Short-Term Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	31	109
Pension Plan [Member] | Cash and Short-Term Investments [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	31	109
Pension Plan [Member] | U.S. Government and Agencies Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	30	25
Pension Plan [Member] | U.S. Government and Agencies Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	30	25
Pension Plan [Member] | Corporate Debt [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	222	188
Pension Plan [Member] | Corporate Debt [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	222	188
Pension Plan [Member] | State and Municipal Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	8	5
Pension Plan [Member] | State and Municipal Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	8	5
Pension Plan [Member] | Foreign Corporate Debt [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	21	20
Pension Plan [Member] | Foreign Corporate Debt [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	21	20
Pension Plan [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	598	449
Pension Plan [Member] | Mutual Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	598	449
Pension Plan [Member] | Pooled Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	1,069	1,168
Pension Plan [Member] | Pooled Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	1,069	1,168
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	1,265	1,218
OPEB [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	1,186	1,141
OPEB [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	526	458
OPEB [Member] | Fair Value, Inputs, Level 1 [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	494	428
OPEB [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	739	760
OPEB [Member] | Fair Value, Inputs, Level 2 [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	692	713
OPEB [Member] | Cash and Short-Term Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	19	44
OPEB [Member] | Cash and Short-Term Investments [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	18	41
OPEB [Member] | Cash and Short-Term Investments [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	19	44
OPEB [Member] | Cash and Short-Term Investments [Member] | Fair Value, Inputs, Level 1 [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	18	41
OPEB [Member] | U.S. Government and Agencies Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	5	3
OPEB [Member] | U.S. Government and Agencies Securities [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	4	3
OPEB [Member] | U.S. Government and Agencies Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	5	3
OPEB [Member] | U.S. Government and Agencies Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	4	3
OPEB [Member] | Corporate Debt [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	33	26
OPEB [Member] | Corporate Debt [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	31	25
OPEB [Member] | Corporate Debt [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	33	26
OPEB [Member] | Corporate Debt [Member] | Fair Value, Inputs, Level 2 [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	31	25
OPEB [Member] | State and Municipal Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	1	1
OPEB [Member] | State and Municipal Bonds [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	1	1
OPEB [Member] | State and Municipal Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	1	1
OPEB [Member] | State and Municipal Bonds [Member] | Fair Value, Inputs, Level 2 [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	1	1
OPEB [Member] | Foreign Corporate Debt [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	3	3
OPEB [Member] | Foreign Corporate Debt [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	3	3
OPEB [Member] | Foreign Corporate Debt [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	3	3
OPEB [Member] | Foreign Corporate Debt [Member] | Fair Value, Inputs, Level 2 [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	3	3
OPEB [Member] | Common Stocks [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	69	71
OPEB [Member] | Common Stocks [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	65	66
OPEB [Member] | Common Stocks [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	69	71
OPEB [Member] | Common Stocks [Member] | Fair Value, Inputs, Level 1 [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	65	66
OPEB [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	438	343
OPEB [Member] | Mutual Funds [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	411	321
OPEB [Member] | Mutual Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	438	343
OPEB [Member] | Mutual Funds [Member] | Fair Value, Inputs, Level 1 [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	411	321
OPEB [Member] | Pooled Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	697	727
OPEB [Member] | Pooled Funds [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	653	681
OPEB [Member] | Pooled Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	697	727
OPEB [Member] | Pooled Funds [Member] | Fair Value, Inputs, Level 2 [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assets for Plan Benefits	$ 653	$ 681