Stockholder's Equity - Accumulated Other Comprehensive Income (Loss) (Tables)

9 Months Ended

Sep. 30, 2025

Equity [Abstract]

Changes in Accumulated Other Comprehensive Loss

	Defined Benefit		Commodity		Interest Rate
	Pension and		Contract		Swap
	Postretirement		Cash Flow		Cash Flow
	Plan Items		Hedges		Hedges		Total
(in millions)
As of December 31, 2024	$	(2.1)	$	0.4	$	—	$	(1.7)
Other comprehensive loss before reclassifications	—		—		(0.8)		(0.8)
Amounts reclassified from accumulated other comprehensive loss	—		(0.5)		(0.2)		(0.7)
Net current-period other comprehensive loss	—		(0.5)		(1.0)		(1.5)
As of September 30, 2025	$	(2.1)	$	(0.1)	$	(1.0)	$	(3.2)

As of December 31, 2023	$	(2.6)	$	(0.3)	$	0.1	$	(2.8)
Other comprehensive income (loss) before reclassifications	—		1.0		(1.3)		(0.3)
Amounts reclassified from accumulated other comprehensive loss	—		(0.6)		(0.4)		(1.0)
Net prior-period other comprehensive income (loss)	—		0.4		(1.7)		(1.3)
As of September 30, 2024	$	(2.6)	$	0.1	$	(1.6)	$	(4.1)