Commitments and Contingencies Nuclear Fuel Disposal (Details)	Dec. 31, 2019 Canister
Monticello [Member]
Loss Contingencies [Line Items]
Number Of Authorized Canisters Filled And Placed In Dry Cask Nuclear Storage Facility	30
Prairie Island [Member]
Loss Contingencies [Line Items]
Number Of Authorized Canisters Filled And Placed In Dry Cask Nuclear Storage Facility	44
Number Of Authorized Canisters In Dry Cask Nuclear Storage Facility	64