Fair Value of Financial Assets and Liabilities Commodity Derivatives (Details) MWh in Millions, MMBTU in Millions, $ in Millions		Jun. 30, 2020 USD ($) MMBTU MWh	Dec. 31, 2019 MMBTU MWh
Cash flow hedge commodity
Derivative [Line Items]
Commodity contracts designated as cash flow hedges | $		$ 0.0
Electric commodity
Gross Notional Amounts of Commodity Forwards, Options and FTRs [Abstract]
Derivative, Nonmonetary Notional amount | MWh	[1],[2]	95.3	79.1
Natural gas commodity
Gross Notional Amounts of Commodity Forwards, Options and FTRs [Abstract]
Derivative, Nonmonetary Notional amount | MMBTU	[1],[2]	82.9	77.8

[1] Amounts are not reflective of net positions in the underlying commodities.

[2] Notional amounts for options are included on a gross basis, but are weighted for the probability of exercise.