Income Tax Expense - Schedule of Income Tax Expense (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Current Income Tax Expense
Federal	$ 3.5	$ 5.6
State	3.4	2.2
Total Current Income Tax Expense	6.9	7.8
Deferred Income Tax Expense (Benefit)
Federal	(5.0)	(8.3)
State	2.4	2.1
Investment Tax Credit Amortization	(0.3)	(0.1)
Total Deferred Income Tax Benefit	(2.9)	(6.3)
Total Income Tax Expense	$ 4.0	$ 1.5