Reportable Business Segments and International Operations, Reconciliation of Segment Operating Income (Details) - USD ($) $ in Millions	3 Months Ended									12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of segment operating income to consolidated income before income taxes
Segment operating income	$ 457.6	$ 444.2	$ 408.2	$ 376.9	$ 399.4	$ 377.9	$ 336.2	$ 314.1		$ 1,686.9	$ 1,427.6	$ 1,205.2
Interest expense										(101.7)	(92.3)	(72.6)
Other income, net										3.2	17.1	8.5
Stock-based compensation expense										(55.6)	(49.7)	(47.6)
Acquisition-related expenses	$ (8.5)						$ (4.0)		$ (6.3)	(8.5)	(4.0)	(36.6)
Other operating expenses										(54.1)	(48.1)	(43.7)
Income before income taxes										1,588.4	1,352.4	1,141.1
Operating Segment
Reconciliation of segment operating income to consolidated income before income taxes
Segment operating income										$ 1,805.1	$ 1,529.4	$ 1,333.1