CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Net income (loss)	$ 665.7	$ 737.3	$ (173.7)
Pension Plan and Restoration of Retirement Income Plan:
Amortization of prior service cost, net of tax of $0.1, $0.0 and $0.0, respectively	0.2	0.1	0.0
Amortization of deferred net loss, net of tax of $0.2, $0.9 and $1.2, respectively	1.4	1.6	3.9
Net gain (loss) arising during the period, net of tax of ($2.4), $0.0 and ($1.7), respectively	(7.6)	1.4	(5.1)
Prior service cost arising during the period, net of tax of $0.0, ($0.3) and $0.0, respectively	0.0	(1.1)	0.0
Settlement cost, net of tax of $4.3, $2.7 and $0.7, respectively	13.6	6.0	2.2
Postretirement benefit plans:
Amortization of prior service credit, net of tax of ($0.1), ($0.4) and ($0.6), respectively	(0.2)	(1.4)	(1.7)
Amortization of deferred net (gain) loss, net of tax of $0.0, $0.0 and $0.0, respectively	0.0	0.1	(0.1)
Net gain (loss) arising during the period, net of tax of $1.7, ($0.2) and ($0.8), respectively	5.5	(0.7)	(2.4)
Curtailment cost, net of tax of $0.0, $0.0 and ($0.1), respectively	0.0	0.0	(0.3)
Other comprehensive gain (loss) from unconsolidated affiliates, net of tax $0.0, $0.3 and ($0.2), respectively	0.0	1.3	(0.7)
Other comprehensive income (loss), net of tax	12.9	7.3	(4.2)
Comprehensive income (loss)	$ 678.6	$ 744.6	$ (177.9)