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Retirement Benefits (Schedule Of Allocation Of Plan Assets) (Details) - USD ($)
$ in Millions
Dec. 31, 2015
Dec. 31, 2014
Pension Plan [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Defined Benefit Plan, Assets for Plan Benefits $ 2,013 $ 1,979
Pension Plan [Member] | Fair Value, Inputs, Level 1 [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Defined Benefit Plan, Assets for Plan Benefits 753 629
Pension Plan [Member] | Fair Value, Inputs, Level 2 [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Defined Benefit Plan, Assets for Plan Benefits 1,260 1,350
Pension Plan [Member] | Cash and Short-Term Investments [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Defined Benefit Plan, Assets for Plan Benefits 215 31
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 215 31
Pension Plan [Member] | U.S. Government and Agencies Securities [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Defined Benefit Plan, Assets for Plan Benefits 19 30
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 19 30
Pension Plan [Member] | Corporate Debt [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Defined Benefit Plan, Assets for Plan Benefits 243 222
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 243 222
Pension Plan [Member] | State and Municipal Bonds [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Defined Benefit Plan, Assets for Plan Benefits 8 8
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 8
Pension Plan [Member] | Foreign Corporate Debt [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Defined Benefit Plan, Assets for Plan Benefits 16 21
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 16 21
Pension Plan [Member] | Mutual Funds [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Defined Benefit Plan, Assets for Plan Benefits 538 598
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 538 598
Pension Plan [Member] | Pooled Funds [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Defined Benefit Plan, Assets for Plan Benefits 974 1,069
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 974 1,069
OPEB [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Defined Benefit Plan, Assets for Plan Benefits 1,208 1,265
OPEB [Member] | Consumers Energy Company [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Defined Benefit Plan, Assets for Plan Benefits 1,133 1,186
OPEB [Member] | Fair Value, Inputs, Level 1 [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Defined Benefit Plan, Assets for Plan Benefits 561 526
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 526 494
OPEB [Member] | Fair Value, Inputs, Level 2 [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Defined Benefit Plan, Assets for Plan Benefits 647 739
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 607 692
OPEB [Member] | Cash and Short-Term Investments [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Defined Benefit Plan, Assets for Plan Benefits 51 19
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 48 18
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 51 19
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 48 18
OPEB [Member] | U.S. Government and Agencies Securities [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Defined Benefit Plan, Assets for Plan Benefits 3 5
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 3 4
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 3 5
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 3 4
OPEB [Member] | Corporate Debt [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Defined Benefit Plan, Assets for Plan Benefits 34 33
OPEB [Member] | Corporate Debt [Member] | Consumers Energy Company [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Defined Benefit Plan, Assets for Plan Benefits 32 31
OPEB [Member] | Corporate Debt [Member] | Fair Value, Inputs, Level 2 [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Defined Benefit Plan, Assets for Plan Benefits 34 33
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 32 31
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 2 3
OPEB [Member] | Foreign Corporate Debt [Member] | Consumers Energy Company [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Defined Benefit Plan, Assets for Plan Benefits 2 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 2 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 2 3
OPEB [Member] | Common Stocks [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Defined Benefit Plan, Assets for Plan Benefits 54 69
OPEB [Member] | Common Stocks [Member] | Consumers Energy Company [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Defined Benefit Plan, Assets for Plan Benefits 51 65
OPEB [Member] | Common Stocks [Member] | Fair Value, Inputs, Level 1 [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Defined Benefit Plan, Assets for Plan Benefits 54 69
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 51 65
OPEB [Member] | Mutual Funds [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Defined Benefit Plan, Assets for Plan Benefits 456 438
OPEB [Member] | Mutual Funds [Member] | Consumers Energy Company [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Defined Benefit Plan, Assets for Plan Benefits 427 411
OPEB [Member] | Mutual Funds [Member] | Fair Value, Inputs, Level 1 [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Defined Benefit Plan, Assets for Plan Benefits 456 438
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 427 411
OPEB [Member] | Pooled Funds [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Defined Benefit Plan, Assets for Plan Benefits 607 697
OPEB [Member] | Pooled Funds [Member] | Consumers Energy Company [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Defined Benefit Plan, Assets for Plan Benefits 569 653
OPEB [Member] | Pooled Funds [Member] | Fair Value, Inputs, Level 2 [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Defined Benefit Plan, Assets for Plan Benefits 607 697
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 $ 569 $ 653