Income Tax Expense - Schedule of Income Tax Expense (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Current Income Tax Expense
Federal	$ 4.0	$ 0.0	$ 12.6	$ 0.0
State	1.1	0.2	6.5	0.3
Total Current Income Tax Expense	5.1	0.2	19.1	0.3
Deferred Income Tax Expense (Benefit)
Federal	5.2	(8.4)	(10.9)	(20.7)
State	9.1	1.1	12.5	1.4
Investment Tax Credit Amortization	(0.1)	(0.1)	(0.3)	(0.4)
Total Deferred Income Tax Expense (Benefit)	14.2	(7.4)	1.3	(19.7)
Total Income Tax Expense (Benefit)	$ 19.3	$ (7.2)	$ 20.4	$ (19.4)