Financial Instruments (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Summary of financial assets with original maturities of less than 90 days included within cash and cash equivalents
Cash equivalents	$ 645.1	$ 2,039.6
Commercial paper
Summary of financial assets with original maturities of less than 90 days included within cash and cash equivalents
Cash equivalents	71.9	31.0
Money market funds
Summary of financial assets with original maturities of less than 90 days included within cash and cash equivalents
Cash equivalents	519.2	741.7
Short-term debt securities
Summary of financial assets with original maturities of less than 90 days included within cash and cash equivalents
Cash equivalents	$ 54.0	$ 1,266.9