Income Taxes (Details)		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019
Income Tax Examination [Line Items]
Federal statutory rate		21.00%	21.00%
State tax (net of federal tax effect)		7.10%	7.10%
Wind PTCs		(24.80%)	(14.40%)
Plant regulatory differences (a)	[1]	(8.30%)	(8.20%)
Other tax credits, net of NOL & tax credit allowances		(1.50%)	(1.30%)
Other (net)		1.00%	0.80%
Effective income tax rate		(5.50%)	5.00%

[1] Regulatory differences for income tax primarily relate to the credit of excess deferred taxes to customers through the average rate assumption method