Long-Lived Assets - Computer Software and Goodwill (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2021	Mar. 31, 2021		Jun. 30, 2020	Mar. 31, 2020
Computer Software
Balance at beginning of period	$ 508.1	$ 437.0	[1]	$ 379.3	$ 382.2
Acquisitions	(1.0)	65.0		0.0	0.0
Additions at cost	33.9	42.2		29.5	18.2
Amortization	(26.6)	(24.5)		(17.0)	(16.0)
Write-off	(0.7)	(3.1)		(0.1)	(0.2)
Other	2.8	(8.5)		2.3	(4.9)
Balance at end of period	516.5	508.1		394.0	379.3
Goodwill
Balance at beginning of period	3,318.2	2,857.9	[1]	2,848.7	2,841.7
Acquisitions	2.6	488.4		0.0	10.7
Other	10.3	(28.1)		0.1	(3.7)
Balance at end of period	$ 3,331.1	$ 3,318.2		$ 2,848.8	$ 2,848.7

[1] See discussion in Note 1 - Basis of Presentation for further detail regarding the elimination of the International lag reporting.