Pension and Other Postretirement Benefits - Changes in Plan Assets & Benefit Obligation Recognized in OCI (pre-taxed) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Net loss (gain)	$ 6.8	$ 7.2	$ 9.5
Prior service cost (benefit)	0.6	(27.4)	0.0
Amortization of prior service (cost) benefit, including recognition due to curtailment	7.1	4.9	2.7
Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net loss (gain)	17.6	(7.5)
Prior service cost (benefit)	0.5	0.0
Amortization of net loss, including recognition due to settlement	(5.2)	(4.7)
Amortization of prior service (cost) benefit, including recognition due to curtailment	(0.1)	(0.1)
Total amount recognized in other comprehensive loss	12.8	(12.3)
Net periodic benefit cost	0.9	3.5	4.5
Total recognized in net periodic benefit cost and other comprehensive loss	13.7	(8.8)
Other Postretirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net loss (gain)	(10.5)	14.7
Prior service cost (benefit)	0.1	(27.4)
Amortization of net loss, including recognition due to settlement	(4.0)	(3.9)
Amortization of prior service (cost) benefit, including recognition due to curtailment	7.2	5.1
Total amount recognized in other comprehensive loss	(7.2)	(11.5)
Net periodic benefit cost	1.2	4.9	$ 7.4
Total recognized in net periodic benefit cost and other comprehensive loss	$ (6.0)	$ (6.6)