Fair Value of Financial Assets and Liabilities Commodity Derivatives (Details) MWh in Millions, MMBTU in Millions, $ in Millions		12 Months Ended
		Dec. 31, 2019 USD ($) MMBTU MWh	Dec. 31, 2018 MMBTU MWh
Derivative [Line Items]
Commodity contracts designated as cash flow hedges		$ 0
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months		$ 0
Electric Commodity
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MWh	[1],[2]	95	87
Natural Gas Commodity
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBTU	[1],[2]	110	92

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

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