Commitments, Guarantees and Contingencies - Transmission (Details) $ in Millions |
Dec. 31, 2019
USD ($)
Miles
kV
MW
|
|---|---|
| Great Northern Transmission Line [Member] | |
| Transmission [Line Items] | |
| Total Project Costs Incurred to Date | $ 633.3 |
| Manitoba Hydro [Member] | Great Northern Transmission Line [Member] | |
| Transmission [Line Items] | |
| Project Costs Recovered from Counterparty | $ 339.6 |
| Minnesota Power [Member] | Great Northern Transmission Line [Member] | |
| Transmission [Line Items] | |
| Transmission Line Length (Miles) | Miles | 220 |
| Transmission Line Capacity (kV) | kV | 500 |
| Total Project Cost in the U.S. | $ 325.0 |
| Minnesota Power [Member] | Great Northern Transmission Line [Member] | Maximum [Member] | |
| Transmission [Line Items] | |
| Total Project Cost in the U.S. | $ 700.0 |
| Manitoba Hydro PPA [Member] | Manitoba Hydro [Member] | |
| Transmission [Line Items] | |
| Output Being Purchased (MW) | MW | 250 |