Summary of Significant Accounting Policies - Summary of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Accumulated other comprehensive income (loss)			$ (7.2)	$ (11.9)
Amounts reclassified from accumulated other comprehensive income (loss)			0.1	0.5
Settlement cost	$ 0.0	$ 0.2	0.0	1.1
Regulatory classification of certain pension costs			3.9
Accumulated other comprehensive income (loss)	(3.2)	(10.3)	(3.2)	(10.3)
Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss) [Member] | Pension Plan [Member]
Accumulated other comprehensive income (loss)			(12.9)	(18.5)
Amounts reclassified from accumulated other comprehensive income (loss)			0.2	0.6
Settlement cost				1.1
Regulatory classification of certain pension costs			3.9
Accumulated other comprehensive income (loss)	(8.8)	(16.8)	(8.8)	(16.8)
Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss) [Member] | Other Postretirement Benefits Plan [Member]
Accumulated other comprehensive income (loss)			5.7	6.6
Amounts reclassified from accumulated other comprehensive income (loss)			(0.1)	(0.1)
Settlement cost				0.0
Regulatory classification of certain pension costs			0.0
Accumulated other comprehensive income (loss)	$ 5.6	$ 6.5	$ 5.6	$ 6.5