Income Taxes (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Federal statutory rate, percent	21.00%	21.00%
State tax (net of federal tax effect), percent	2.40%	2.20%
Wind PTCs, percent	(15.60%)	(3.90%)
Plant regulatory differences, percent	(6.20%)	(4.70%)
Effective Income Tax Rate Reconciliation, Prior Year Income Taxes, Percent	(1.50%)	(0.50%)
Other tax credits, percent	(0.70%)	(0.60%)
Other (net), percent	(0.30%)	(0.50%)
Effective income tax rate, percent	(0.90%)	13.00%
Federal income tax adjustment	$ 0
State income tax adjustment	$ 0