CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Statement of Comprehensive Income [Abstract]
Net income	$ 38.3	$ 279.5
Pension Plan and Restoration of Retirement Income Plan:
Amortization of prior service cost, net of tax of $0.0 and $0.0, respectively	0.1	0.1
Amortization of deferred net loss, net of tax of $0.1 and $0.1, respectively	0.2	0.3
Settlement cost, net of tax of $0.2 and $2.2, respectively	0.9	7.4
Postretirement benefit plans:
Amortization of deferred net gain, net of tax of $0.0 and $0.0, respectively	(0.1)	0.0
Other comprehensive income, net of tax	1.1	7.8
Comprehensive income	$ 39.4	$ 287.3