Goodwill and Intangible Assets - Changes in Carrying Value (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Finite-lived Intangible Assets [Roll Forward]
Accumulated Amortization, Beginning Balance			$ (545.9)
Amortization expense	$ (30.9)	$ (30.9)	(92.7)	$ (92.8)
Retirements, net			(1.0)
Accumulated Amortization, Ending Balance	(638.0)		(638.0)
Net Carrying Amount, Ending Balance	1,156.2		1,156.2
Customer relationships
Finite-lived Intangible Assets [Roll Forward]
Gross Carrying Amount, Beginning Balance			1,795.8
Accumulated Amortization, Beginning Balance			(545.9)
Net Carrying Amount, Beginning Balance			1,249.9
Amortization expense			(92.7)
Retirements, gross			(1.6)
Retirements, accumulated amortization			0.6
Gross Carrying Amount, Ending Balance	1,794.2		1,794.2
Accumulated Amortization, Ending Balance	(638.0)		(638.0)
Net Carrying Amount, Ending Balance	$ 1,156.2		$ 1,156.2