CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME Parenthetical - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Plan and Restoration of Retirement Income Plan:
Amortization of deferred net loss, net of tax of $1.1, $1.4 and $1.7, respectively	$ 1.1	$ 1.4	$ 1.7
Net gain (loss) arising during the period, net of tax of ($4.7), $0.2 and ($0.6), respectively	(4.7)	0.2	(0.6)
Amortization of prior service cost, net of tax of $0.0, $0.0 and $0.0, respectively	0.0	0.0	0.0
Postretirement plans:
Prior service cost arising during the period, net of tax of $0.0, $4.0 and $0.0, respectively	0.0	(4.0)	0.0
Amortization of deferred net loss, net of tax of $0.0, $0.0 and $0.0, respectively	0.0	0.0	0.0
Net gain (loss) arising during the period, net of tax of $0.7, ($0.2) and $0.1, respectively	0.7	(0.2)	0.1
Amortization of prior service credit, net of tax of ($0.6), ($0.3) and ($1.0), respectively	(0.6)	(0.3)	(1.0)
Amortization of deferred interest rate swap hedging losses, net of tax of $0, $0 and $0.0, respectively	0.0	0.0	0.0
Pension Plans [Member]
Pension Plan and Restoration of Retirement Income Plan:
Settlement cost, net of tax of $1.6, $1.4 and $3.2, respectively	1.6	1.4	3.2
Other Postretirement Benefits Plan [Member]
Pension Plan and Restoration of Retirement Income Plan:
Settlement cost, net of tax of $1.6, $1.4 and $3.2, respectively	$ 0.0	$ 0.2
Postretirement plans:
Settlement cost, net of tax of $0.0, $0.2 and $0.0, respectively			$ 0.0