Intangible Assets - Changes in Carrying Value (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Finite-lived Intangible Assets [Roll Forward]
Accumulated Amortization, Beginning Balance			$ (668.8)
Customer relationships obtained from acquisition of business			57.3
Amortization expense	$ (31.6)	$ (30.9)	(62.5)	$ (61.8)
Accumulated Amortization, Ending Balance	(731.3)		(731.3)
Net Carrying Amount, Ending Balance	1,120.2		1,120.2
Customer relationships
Finite-lived Intangible Assets [Roll Forward]
Gross Carrying Amount, Beginning Balance			1,794.2
Accumulated Amortization, Beginning Balance			(668.8)
Net Carrying Amount, Beginning Balance			1,125.4
Amortization expense			(62.5)
Gross Carrying Amount, Ending Balance	1,851.5		1,851.5
Accumulated Amortization, Ending Balance	(731.3)		(731.3)
Net Carrying Amount, Ending Balance	$ 1,120.2		$ 1,120.2