Retirement Benefits (Narrative) (Details)
$ in Millions |
9 Months Ended |
|
Sep. 30, 2016
USD ($)
|
|---|
| DB Pension Plan [Member] |
|
| Defined Benefit Plan Disclosure [Line Items] |
|
| Decrease in service cost and interest expense |
$ 17
|
| OPEB [Member] |
|
| Defined Benefit Plan Disclosure [Line Items] |
|
| Decrease in service cost and interest expense |
9
|
| Consumers Energy Company [Member] | DB Pension Plan [Member] |
|
| Defined Benefit Plan Disclosure [Line Items] |
|
| Decrease in service cost and interest expense |
17
|
| Consumers Energy Company [Member] | OPEB [Member] |
|
| Defined Benefit Plan Disclosure [Line Items] |
|
| Decrease in service cost and interest expense |
$ 9
|