Unaudited Consolidated Statement of Stockholders' Equity - USD ($) shares in Millions, $ in Millions	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Income, Net of Tax	Noncontrolling Interests In Consolidated Subsidiary
Balance (in shares) at Dec. 31, 2017		350.1			18.4
Balance at Dec. 31, 2017	$ 7,961.1	$ 3.5	$ 4,839.6	$ 4,152.5	$ (1,059.4)	$ 22.6	$ 2.3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	237.9			237.7			0.2
Other comprehensive income (loss)	19.1					19.1
Cash dividends declared	(113.3)			(113.3)
Issuances of common stock (in shares)		(1.0)			(0.3)
Issuances of common stock	1.3		20.6		$ (19.3)
Stock-based compensation	10.4		11.4	(1.0)
Purchase of common stock for treasury (in shares)					(3.8)
Purchase of common stock for treasury	(235.6)				$ (235.6)
Balance (in shares) at Mar. 31, 2018		351.1			22.5
Balance at Mar. 31, 2018	7,914.3	$ 3.5	4,871.6	4,309.3	$ (1,314.3)	41.7	2.5
Balance (in shares) at Dec. 31, 2018		351.9			29.4
Balance at Dec. 31, 2018	7,929.5	$ 3.5	4,924.9	4,750.5	$ (1,782.6)	30.8	2.4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of accounting standards	5.4			(5.4)		5.4
Net income	234.9			234.2			0.7
Other comprehensive income (loss)	(11.4)					(11.4)
Cash dividends declared	(120.7)			(120.7)
Issuances of common stock (in shares)		(0.9)			(0.2)
Issuances of common stock	(9.1)		7.7		$ (16.8)
Stock-based compensation	10.9		12.0	(1.1)
Purchase of common stock for treasury (in shares)					(1.5)
Purchase of common stock for treasury	(111.5)				$ (111.5)
Balance (in shares) at Mar. 31, 2019		352.8			31.1
Balance at Mar. 31, 2019	$ 7,922.6	$ 3.5	$ 4,944.6	$ 4,857.5	$ (1,910.9)	$ 24.8	$ 3.1