Pensions and Other Postretirement Benefits - Additional Disclosures (Details) $ in Millions	3 Months Ended			12 Months Ended
	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2019 USD ($) plan	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Multiemployer Plan
Multiemployer plans, plan contributions				$ 0.6	$ 3.4
Multiemployer withdrawal liability		$ 30.8		$ 30.8	32.4
Number of multiemployer plans | plan				1
Percent of total plan contributions for the most recent plan year				5.00%
Defined Contribution Plans
Contributions to defined contribution plans				$ 57.6	54.6	$ 37.7
NACP Combination
Defined Contribution Plans
Increase in contribution to defined contribution plan					16.9
Forecast
Defined Benefit Plan Disclosure [Line Items]
Transfer of remaining pension benefit obligation to annuity	$ 750.0
Pension Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Transfer of remaining pension benefit obligation to annuity				$ 150.2	$ 0.0
Weighted average discount rate		2.69%		2.69%	4.14%
Accumulated benefit obligation (ABO)		$ 1,249.8		$ 1,249.8	$ 1,240.2
Aggregate ABO of plan assets		1,043.0		1,043.0
Aggregate PBO of plan assets		1,048.6		1,048.6
Aggregate fair value of plan assets		$ 942.9		942.9
Company's contributions to its pension plans				11.3	5.8
Benefit payments made				67.2	65.4
Posretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Transfer of remaining pension benefit obligation to annuity				$ 0.0	$ 0.0
Weighted average discount rate		3.22%		3.22%	4.29%
Company's contributions to its pension plans				$ 1.2	$ 1.9
Benefit payments made				1.2	$ 1.9
Expected contributions in 2019		$ 3.0		3.0
Minimum | Pension Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Expected contributions in 2019		10.0		10.0
Maximum | Pension Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Expected contributions in 2019		20.0		20.0
UNITED KINGDOM
Defined Benefit Plan Disclosure [Line Items]
Contributions to defined benefit plans			$ 6.8
UNITED STATES
Defined Benefit Plan Disclosure [Line Items]
Contributions to defined benefit plans			$ 75.0
Lump sum payments		150.2
Net actuarial loss		39.2
UNITED STATES | Forecast
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	$ 150.0
PIUMPF
Multiemployer Plan
Multiemployer withdrawal liability		4.4		4.4
Graphic Communications Conference of International Brotherhood of Teamster Pension Fund
Multiemployer Plan
Multiemployer withdrawal liability		$ 4.4		$ 4.4
Corporate Debt Securities | Minimum
Defined Benefit Plan Disclosure [Line Items]
Debt securities maturity term		1 year		1 year
Corporate Debt Securities | Maximum
Defined Benefit Plan Disclosure [Line Items]
Debt securities maturity term		30 years		30 years