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Retirement Benefits (Schedule Of Expected Benefit Payments) (Details)
$ in Millions
Dec. 31, 2015
USD ($)
Pension Plan [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Benefit Payments, 2016 $ 141
Benefit Payments, 2017 146
Benefit Payments, 2018 152
Benefit Payments, 2019 156
Benefit Payments, 2020 159
Benefit Payments, 2021-2025 815
Pension Plan [Member] | Consumers Energy Company [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Benefit Payments, 2016 137
Benefit Payments, 2017 142
Benefit Payments, 2018 148
Benefit Payments, 2019 152
Benefit Payments, 2020 155
Benefit Payments, 2021-2025 793
DB SERP [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Benefit Payments, 2016 8
Benefit Payments, 2017 8
Benefit Payments, 2018 8
Benefit Payments, 2019 9
Benefit Payments, 2020 10
Benefit Payments, 2021-2025 50
DB SERP [Member] | Consumers Energy Company [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Benefit Payments, 2016 5
Benefit Payments, 2017 5
Benefit Payments, 2018 5
Benefit Payments, 2019 5
Benefit Payments, 2020 6
Benefit Payments, 2021-2025 30
OPEB [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Benefit Payments, 2016 53
Benefit Payments, 2017 57
Benefit Payments, 2018 59
Benefit Payments, 2019 63
Benefit Payments, 2020 65
Benefit Payments, 2021-2025 353
OPEB [Member] | Consumers Energy Company [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Benefit Payments, 2016 51
Benefit Payments, 2017 55
Benefit Payments, 2018 57
Benefit Payments, 2019 61
Benefit Payments, 2020 63
Benefit Payments, 2021-2025 $ 341