Fair Value Measurement (Assets and Liabilities Measured on a Recurring Basis) (Details) - Recurring Basis - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Level 1
Financial assets:
Marketable equity securities	$ 89.7	$ 65.8
Marketable debt securities	3.8	3.6
Derivative instruments	0.0	0.0
Total assets	93.5	69.4
Financial liabilities:
Joint venture net written option	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	14.1	11.9
Derivative instruments	17.9	18.0
Total assets	32.0	29.9
Financial liabilities:
Joint venture net written option	0.0
Derivative instruments	14.2	8.3
Contingent consideration payable	0.0	0.0
Total liabilities	14.2	8.3
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	40.0
Derivative instruments	0.0	0.0
Contingent consideration payable	1,168.2	1,058.0
Total liabilities	1,208.2	1,058.0
Fair value
Financial assets:
Marketable equity securities	89.7	65.8
Marketable debt securities	17.9	15.5
Derivative instruments	17.9	18.0
Total assets	125.5	99.3
Financial liabilities:
Joint venture net written option	40.0
Derivative instruments	14.2	8.3
Contingent consideration payable	1,168.2	1,058.0
Total liabilities	$ 1,222.4	$ 1,066.3