Contingencies And Commitments (Expected Remediation Cost By Year) (Details) $ in Millions |
Sep. 30, 2016
USD ($)
|
|---|---|
| Bay Harbor [Member] | |
| Site Contingency [Line Items] | |
| Undiscounted amount due within one year | $ 5 |
| Undiscounted amount due within two year | 5 |
| Undiscounted amount due within third year | 4 |
| Undiscounted amount due within fourth year | 4 |
| Undiscounted amount due within five year | 4 |
| Gas Utility [Member] | Manufactured Gas Plant [Member] | Consumers Energy Company [Member] | |
| Site Contingency [Line Items] | |
| Undiscounted amount due within one year | 6 |
| Undiscounted amount due within two year | 35 |
| Undiscounted amount due within third year | 14 |
| Undiscounted amount due within fourth year | 19 |
| Undiscounted amount due within five year | $ 10 |