Fair Value Measurements - Schedule of Changes in Level 3 Assets and Liabilities (Details) - Level 3 [Member] - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period - assets	$ 350.0	$ 296.1
Total realized and unrealized gains (losses) - assets	3.2	2.0
Purchases - assets	17.9	11.1
Sales - assets	(6.3)	(14.9)
Transfers out of Level 3 - assets	(29.0)	0.0
Balance at End of Period - assets	333.7	295.8
Change in unrealized gains (losses) included in net income relating to assets and liability held at end of period - assets	10.3	1.1
Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period - assets	32.6	199.9
Purchases - assets	0.0	5.3
Sales - assets	(4.3)	0.0
Transfers out of Level 3 - assets	(2.1)	0.0
Foreign exchange revaluation and other	0.0	3.7
Balance at End of Period - assets	29.0	210.1
Change in unrealized gains (losses) included in net income relating to assets and liability held at end of period - assets	2.8	1.2
Contingent Consideration Liability [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period - liability	(38.7)	(51.0)
Purchases - liability	0.0	0.0
Sales - liability	0.0	0.0
Transfers out of Level 3 - liability	0.0	0.0
Foreign exchange revaluation and other	0.0	(7.0)
Balance at End of Period - liability	(40.0)	(62.0)
Change in unrealized gains (losses) included in net income relating to assets and liability held at end of period - liability	(1.3)	(4.0)
Investment and other income [Member] | Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total realized and unrealized gains (losses) - assets	2.8	1.2
Investment and other income [Member] | Contingent Consideration Liability [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total realized and unrealized gains (losses) - liability	0.0	0.0
General, administrative and other expense [Member] | Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total realized and unrealized gains (losses) - assets	0.0	0.0
General, administrative and other expense [Member] | Contingent Consideration Liability [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total realized and unrealized gains (losses) - liability	$ (1.3)	$ (4.0)