Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2024	Sep. 30, 2023
Net income	$ 10.3	$ 10.2	$ 2.6	$ 38.6	$ (5.2)	$ 1.2	$ 23.1	$ 34.6
Derivative activity:
Reclassification of earnings, net of income tax	(0.1)			(0.2)			(0.6)	(0.6)
Pension and postretirement activity:
Reclassification to earnings, net of income tax	0.0			0.0			0.1	0.1
Other comprehensive loss	(0.1)	(0.2)	(0.2)	(0.2)	(0.1)	(0.2)	(0.5)	(0.5)
NET COMPREHENSIVE INCOME	10.2			38.4			22.6	34.1
Subsidiaries [Member]
Net income	12.5			43.6	(0.4)	9.6	37.0	52.8
Pension and postretirement activity:
Reclassification to earnings, net of income tax	0.4			0.1			1.2	0.3
Other comprehensive loss	0.4	0.4	0.4	0.1	$ 0.1	$ 0.1	1.2	0.3
NET COMPREHENSIVE INCOME	$ 12.9			$ 43.7			$ 38.2	$ 53.1
Retained Earnings [Member] | Subsidiaries [Member]
Net income		$ 15.1	$ 9.4