Fair Value Measurement (Assets and Liabilities Measured on a Recurring Basis) (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Financial liabilities:
Joint venture net written option	$ 22.5	$ 11.5
Recurring Basis | Level 1
Financial assets:
Marketable equity securities	161.0	89.7
Marketable debt securities	3.6	3.8
Derivative instruments	0.0	0.0
Total assets	164.6	93.5
Financial liabilities:
Joint venture net written option	0.0	0.0
Derivative instruments	0.0	0.0
Contingent consideration payable	0.0	0.0
Total liabilities	0.0	0.0
Recurring Basis | Level 2
Financial assets:
Marketable equity securities	0.0	0.0
Marketable debt securities	13.4	14.1
Derivative instruments	13.9	17.9
Total assets	27.3	32.0
Financial liabilities:
Joint venture net written option	0.0	0.0
Derivative instruments	30.8	14.2
Contingent consideration payable	0.0	0.0
Total liabilities	30.8	14.2
Recurring Basis | Level 3
Financial assets:
Marketable equity securities	0.0	0.0
Marketable debt securities	0.0	0.0
Derivative instruments	0.0	0.0
Total assets	0.0	0.0
Financial liabilities:
Joint venture net written option	48.0	40.0
Derivative instruments	0.0	0.0
Contingent consideration payable	616.2	1,168.2
Total liabilities	664.2	1,208.2
Fair value | Recurring Basis
Financial assets:
Marketable equity securities	161.0	89.7
Marketable debt securities	17.0	17.9
Derivative instruments	13.9	17.9
Total assets	191.9	125.5
Financial liabilities:
Joint venture net written option	48.0	40.0
Derivative instruments	30.8	14.2
Contingent consideration payable	616.2	1,168.2
Total liabilities	$ 695.0	$ 1,222.4