Fair Value Measurement (Assets and Liabilities Measured on a Recurring Basis) (Details) - Recurring Basis - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Level 1
Financial assets:
Marketable equity securities	$ 114.1	$ 89.7
Marketable debt securities	3.9	3.8
Derivative instruments	0.0	0.0
Total assets	118.0	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
Level 2
Financial assets:
Marketable equity securities	0.0	0.0
Marketable debt securities	14.2	14.1
Derivative instruments	17.3	17.9
Total assets	31.5	32.0
Financial liabilities:
Joint venture net written option	0.0	0.0
Derivative instruments	44.3	14.2
Contingent consideration payable	0.0	0.0
Total liabilities	44.3	14.2
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	32.0	40.0
Derivative instruments	0.0	0.0
Contingent consideration payable	1,179.6	1,168.2
Total liabilities	1,211.6	1,208.2
Fair value
Financial assets:
Marketable equity securities	114.1	89.7
Marketable debt securities	18.1	17.9
Derivative instruments	17.3	17.9
Total assets	149.5	125.5
Financial liabilities:
Joint venture net written option	32.0	40.0
Derivative instruments	44.3	14.2
Contingent consideration payable	1,179.6	1,168.2
Total liabilities	$ 1,255.9	$ 1,222.4