Employee Retirement Plans - Summary of Changes in Fair Value of Level 3 Pension Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance	$ 162.8	$ 190.2
Actual return on plan assets	18.7	(11.7)
Benefits paid	(6.8)	(10.0)
Foreign currency gain (loss)	5.7	(9.5)
Ending balance	187.4	162.8
Merchant Navy Officers Pension Fund
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance	160.0
Ending balance	183.9	160.0
Level 3 | Merchant Navy Officers Pension Fund
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance	2.8	3.2
Actual return on plan assets	0.8	(0.1)
Defined Benefit Plan, Plan Assets, Contributions by Employer	0.0	0.0
Benefits paid	(0.3)	(0.1)
Foreign currency gain (loss)	0.2	(0.2)
Ending balance	$ 3.5	$ 2.8