Pension and Other Retiree Benefits (Narrative) (Details) $ in Millions		12 Months Ended
		Dec. 31, 2017 USD ($) yr	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Number of post-retirement plans not frozen to new participants		1
Pension and post-retirement benefit obligations		$ 275.5	$ 98.0
Employer contributions		21.7
Expected contributions to defined benefit plans for 2018		20.0
Costs related to defined contribution plans		13.4	11.3	$ 9.8
Defined Contribution Plan, Increase (Decrease), Cost		$ 2.1	1.5
Minimum
Defined Benefit Plan Disclosure [Line Items]
Payment of retirement benefits, commencement age for participants | yr		60
Maximum
Defined Benefit Plan Disclosure [Line Items]
Payment of retirement benefits, commencement age for participants | yr		65
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation		$ 887.9	536.8
Pension Plan | U.S.
Defined Benefit Plan Disclosure [Line Items]
Pension and post-retirement benefit obligations	[1]	44.4	49.6
Employer contributions		$ 7.3	$ 0.9
Pension Plan | U.S. | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations		60.00%
Pension Plan | U.S. | Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations		28.00%
Pension Plan | U.S. | Alternate assets
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations		12.00%

[1] Pension and post-retirement obligations of $275.5 million as of December 31, 2017, increased from $98.0 million as of December 31, 2016, primarily due to the Esselte Acquisition.