Fair Value Measurements - Schedule of Changes in Level 3 Assets and Liabilities (Details) - Level 3 [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period - assets	$ 17.8	$ 40.2	$ 17.4	$ 32.1
Purchases	3.0	0.0	8.5	12.6
Sales - assets	(1.2)	(2.0)	(5.5)	(3.5)
Settlements - assets	0.0	(0.1)	(0.5)	(2.8)
Consolidation of investment product	0.0	10.0	0.0	10.0
Transfers out of Level 3			(0.2)	0.0
Foreign exchange revaluation	0.0	0.0
Balance at End of Period - assets	19.5	27.7	19.5	27.7
Change in unrealized losses included in net income relating to assets and liability held at end of period - assets	(0.1)	(1.1)	(0.2)	(1.9)
Contingent Consideration Asset
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period - assets	36.9		39.7
Purchases	0.0		0.0
Sales - assets	0.0		0.0
Settlements - assets	(7.8)		(10.6)
Transfers out of Level 3			0.0
Foreign exchange revaluation	0.0
Balance at End of Period - assets	29.1		29.1
Change in unrealized losses included in net income relating to assets and liability held at end of period - assets	0.0		0.0
Contingent Consideration Liabilities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period - liabilities	(25.5)	0.0	(25.3)	0.0
Acquisitions	0.0	(7.6)	0.0	(7.6)
Purchases - liabilities	0.0	0.0	0.0	0.0
Sales - liabilities	0.0	0.0	0.0	0.0
Settlements - liabilities	0.0	0.0	0.0	0.0
Transfers out of Level 3 - liabilities			0.0	0.0
Foreign exchange revaluation	0.2	0.0
Balance at End of Period - liabilities	(25.3)	(7.6)	(25.3)	(7.6)
Change in unrealized losses included in net income relating to assets and liability held at end of period - liabilities	0.0	0.0	0.0	0.0
Investment and other income (losses) [Member] | Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total realized and unrealized gains (losses) - assets	(0.1)	(0.4)	(0.2)	(0.7)
Investment and other income (losses) [Member] | Contingent Consideration Asset
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total realized and unrealized gains (losses) - assets	0.0		0.0
Investment and other income (losses) [Member] | Contingent Consideration Liabilities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total realized and unrealized gains (losses) - liabilities	$ 0.0	$ 0.0	$ 0.0	$ 0.0