Employee Benefits Employee Benefits, Net benefits expected to be paid in each of the next five fiscal years (Details) $ in Millions	Dec. 31, 2017 USD ($)
Defined Benefit Plan Disclosure [Line Items]
2016	$ 7.8
2017	7.6
2018	7.5
2019	7.4
2020	7.1
2020-2023	32.2
VEBAs
Defined Benefit Plan Disclosure [Line Items]
2016	7.5
2017	7.3
2018	7.2
2019	7.0
2020	6.8
2020-2023	30.3
Canadian pension plan | Canadian pension plan
Defined Benefit Plan Disclosure [Line Items]
2016	0.3
2017	0.3
2018	0.3
2019	0.4
2020	0.3
2020-2023	$ 1.9