CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Net income	$ 205.1	$ 183.4	$ 370.8	$ 324.2
Pension Plan and Restoration of Retirement Income Plan:
Amortization of deferred net loss, net of tax of $0.3, $0.5, $0.8 and $1.3, respectively	0.8	0.6	2.5	2.0
Settlement cost, net of tax of $1.1, $0.0 , $1.1 and $0.0, respectively	3.1	0.0	3.1	0.0
Postretirement Benefit Plans:
Prior service cost arising during the period, net of tax of $0.0, $4.1, $0.0 and $4.1, respectively	0.0	6.7	0.0	6.7
Amortization of prior service credit, net of tax of ($0.1), ($0.2), ($0.4) and ($0.2), respectively	(0.5)	(0.2)	(1.3)	(0.2)
Other comprehensive income, net of tax	3.4	7.6	4.3	9.0
Comprehensive income	208.5	191.0	375.1	333.2
Other Comprehensive Income (Loss), Postretirement Plan, Settlement and Curtailment Gain (Loss), after Tax	$ 0.0	$ 0.5	$ 0.0	$ 0.5