Shareholders' Equity (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Amortization of Net Loss [Member]
Amounts recognized as a component of net periodic pension and other postretirement benefit cost:
Total before income taxes	$ (6.1)	$ (5.9)	$ (14.1)	$ (11.8)
Amortization of Prior Service Credit [Member]
Amounts recognized as a component of net periodic pension and other postretirement benefit cost:
Total before income taxes	3.7	4.6	8.2	9.1
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Amounts recognized as a component of net periodic pension and other postretirement benefit cost:
Total before income taxes	(2.4)	(1.3)	(5.9)	(2.7)
Income tax benefit	0.5	0.5	1.2	1.0
Total reclassifications for the period, net of income taxes	$ (1.9)	$ (0.8)	$ (4.7)	$ (1.7)