Summary of Significant Accounting Policies (Effects of Adoption of Topic 606 - Unaudited Consolidated Balance Sheets) (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Other current assets	$ 900.1	$ 795.3
Other current liabilities	237.8	908.8
Other non-current liabilities	2,294.9	2,197.9
Retained earnings	11,452.4	$ 9,920.6
ASU 2014-09 | Before Adoption of Topic 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Other current assets	844.5
Other current liabilities	238.8
Other non-current liabilities	2,296.9
Retained earnings	$ 11,414.5