Retirement Benefits - Narrative (Details)	3 Months Ended		12 Months Ended
	Sep. 30, 2018 USD ($) benefit_plan	Dec. 31, 2016 USD ($) benefit_plan	Dec. 31, 2018 USD ($) benefit_plan	Dec. 31, 2017 USD ($) benefit_plan	Dec. 31, 2016 USD ($) benefit_plan
Defined Benefit Plan Disclosure [Line Items]
Number of foreign plans amended | benefit_plan	1
Accumulated benefit obligation			$ 835,600,000	$ 924,600,000
Number of defined contribution pension plans (benefit plan) | benefit_plan			5
Defined contribution pension plans, total costs			$ 22,500,000	$ 19,800,000	$ 15,600,000
Number of multiemployer defined benefit pension plans (benefit_plan) | benefit_plan		2			2
Number of multiemployer plans withdrawn from | benefit_plan				1
Multiemployer plan total employer contributions			200,000	$ 400,000	$ 500,000
Pre-tax restructuring costs			12,000,000	20,300,000	35,000,000
Expected cost remaining			7,900,000
Employer stock included in plan assets			0	0
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Pension expenses			100,000	100,000	100,000
Benefit obligation		$ 917,400,000	$ 844,300,000	$ 956,100,000	$ 917,400,000
Discount rate		4.12%	4.24%	3.67%	4.12%
Voluntary contributions			$ 20,000,000
Employer contributions			27,900,000
United States | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Curtailment gain					$ 34,100,000
Pension expenses					200,000
Projected benefit obligation settled			$ 28,000,000		$ 40,000,000
Defined benefit obligation per plan, as a percent of total benefit obligation			88.00%
Discount rate			4.40%	3.80%
Canada
Defined Benefit Plan Disclosure [Line Items]
Discount rate			3.60%	3.50%
United Kingdom
Defined Benefit Plan Disclosure [Line Items]
Discount rate			2.90%	2.60%
Foreign Plan
Defined Benefit Plan Disclosure [Line Items]
Curtailment gain	$ 4,700,000
Foreign Plan | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Estimated future employer contributions in next fiscal year			$ 500,000
Withdrawal from Multiemployer Defined Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Pre-tax restructuring costs		$ 12,500,000
Expected cost remaining			$ 23,000,000