Fair Value of Financial Assets and Liabilities Commodity Derivatives (Details) - MWh MWh in Millions		Sep. 30, 2019	Dec. 31, 2018
Electric Commodity [Member]
Derivative [Line Items]
Derivative, Mwh of electricity	[1]	9.4	5.5

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