Fair Value of Financial Assets and Liabilities Commodity Derivatives (Details) - MMBTU MMBTU in Millions		Dec. 31, 2019	Dec. 31, 2018
Natural Gas Commodity
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	[1],[2]	0.1	1.2

[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.