Fair Value Measurement (Assets and Liabilities Measured on a Recurring Basis) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Financial liabilities:
Joint venture net written option	$ 56.4	$ 11.5
Recurring Basis | Level 1
Financial assets:
Marketable equity securities	218.4	89.7
Marketable debt securities	3.7	3.8
Derivative instruments	0.0	0.0
Total assets	222.1	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	13.6	14.1
Derivative instruments	17.7	17.9
Total assets	31.3	32.0
Financial liabilities:
Joint venture net written option	0.0	0.0
Derivative instruments	61.8	14.2
Contingent consideration payable	0.0	0.0
Total liabilities	61.8	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	37.0	40.0
Derivative instruments	0.0	0.0
Contingent consideration payable	1,209.2	1,168.2
Total liabilities	1,246.2	1,208.2
Fair value | Recurring Basis
Financial assets:
Marketable equity securities	218.4	89.7
Marketable debt securities	17.3	17.9
Derivative instruments	17.7	17.9
Total assets	253.4	125.5
Financial liabilities:
Joint venture net written option	37.0	40.0
Derivative instruments	61.8	14.2
Contingent consideration payable	1,209.2	1,168.2
Total liabilities	$ 1,308.0	$ 1,222.4