Income Taxes (Details) - USD ($) $ in Millions		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019
Income Tax Disclosure [Abstract]
Federal statutory rate, percent		21.00%	21.00%
State tax (net of federal tax effect), percent		2.30%	2.10%
Wind PTCs, percent		(26.70%)	(0.20%)
Plant regulatory differences, percent	[1]	(6.40%)	(4.80%)
Effective Income Tax Rate Reconciliation, Prior Year Income Taxes, Percent		(2.00%)	(0.70%)
Other tax credits, percent		(0.70%)	(0.60%)
Other (net), percent		(0.20%)	(0.40%)
Effective income tax rate, percent		(12.70%)	16.40%
Income Tax Credits and Adjustments		$ 0

[1] Regulatory differences for income tax primarily relate to the credit of excess deferred taxes to customers through the average rate assumption method. Income tax benefits associated with the credit of excess deferred credits are offset by corresponding revenue reductions.