Goodwill and Intangible Assets - Computer Software and Goodwill (Details) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022
Computer software
Balance at beginning of period	$ 656.7	$ 642.8	$ 631.8	$ 578.9	$ 563.4	$ 557.4
Additions at cost	39.8	52.2	44.0	57.3	61.9	43.4
Amortization	(39.5)	(37.4)	(34.9)	(30.7)	(31.8)	(30.3)
Impairment / Write-off		(0.9)	(0.3)	(1.1)
Other	(6.1)	0.0	2.2	(15.7)	(14.6)	(7.1)
Balance at end of period	650.9	656.7	642.8	588.7	578.9	563.4
Goodwill
Balance at beginning of period	3,422.4	3,435.7	3,431.3	3,437.1	3,475.4	3,493.3
Other	(8.5)	(13.3)	4.4	(36.3)	(38.3)	(17.9)
Balance at end of period	$ 3,413.9	$ 3,422.4	$ 3,435.7	$ 3,400.8	$ 3,437.1	$ 3,475.4