CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Other comprehensive income (loss), net of tax
Net Income (Loss) Attributable to Parent	$ 252.5	$ 177.4	$ 418.1	$ (228.5)
Pension Plan and Restoration of Retirement Income Plan:
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, after Tax	0.1	0.0	0.1	0.0
Amortization of deferred net loss, net of tax of $0.2, $0.3, $0.6 and $0.9, respectively	0.4	0.9	1.2	2.9
Settlement cost, net of tax of $0.3, $0.5, $1.9 and $0.6, respectively	1.1	1.3	4.8	1.5
Postretirement Benefit Plans:
Amortization of prior service credit, net of tax of ($0.1), ($0.2), ($0.3) and ($0.5), respectively	(0.3)	(0.4)	(1.0)	(1.2)
Amortization of deferred net gain (loss), net of tax of $0.0, $0.0, $0.0 and $0.0, respectively	0.0	0.0	0.1	(0.1)
Other comprehensive gain (loss) from unconsolidated affiliates, net of tax of $0.0, $0.1, $0.1 and ($0.3), respectively	0.3	0.4	0.6	(0.9)
Other comprehensive income (loss), net of tax	1.6	2.2	5.8	2.2
Comprehensive income (loss)	254.1	179.6	423.9	(226.3)
Other Comprehensive Income (Loss), before Tax, Portion Attributable to Noncontrolling Interest	$ 0.0	$ 0.1	$ 0.1	$ (0.3)