Fair Value of Financial Assets and Liabilities Commodity Derivatives (Details) - MMBTU MMBTU in Millions		Mar. 31, 2020	Dec. 31, 2019
Natural Gas Commodity [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	[1],[2]	0.0	0.1

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

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