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 beginning of period 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	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 end of period 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, 2017		350.1			18.4
Balance at beginning of period 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	473.6
Balance (in shares) at Jun. 30, 2018		351.4			25.8
Balance at end of period at Jun. 30, 2018	7,848.8	$ 3.5	4,888.4	4,430.9	$ (1,529.5)	52.8	2.7
Balance (in shares) at Mar. 31, 2018		351.1			22.5
Balance at beginning of period at Mar. 31, 2018	7,914.3	$ 3.5	4,871.6	4,309.3	$ (1,314.3)	41.7	2.5
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	235.7			234.9			0.8
Other comprehensive income	11.1					11.1
Cash dividends declared	(112.4)			(112.4)
Issuances of common stock (in shares)		0.3
Issuances of common stock	6.9		7.1		$ (0.2)
Stock-based compensation	8.8		9.7	(0.9)
Purchase of common stock for treasury (in shares)					(3.3)
Purchase of common stock for treasury	(215.0)				$ (215.0)
Distributions paid	(0.6)						(0.6)
Balance (in shares) at Jun. 30, 2018		351.4			25.8
Balance at end of period at Jun. 30, 2018	7,848.8	$ 3.5	4,888.4	4,430.9	$ (1,529.5)	52.8	2.7
Balance (in shares) at Dec. 31, 2018		351.9			29.4
Balance at beginning of period 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]
Net income	234.9			234.2			0.7
Other comprehensive income	(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 end of period at Mar. 31, 2019	7,922.6	$ 3.5	4,944.6	4,857.5	$ (1,910.9)	24.8	3.1
Balance (in shares) at Dec. 31, 2018		351.9			29.4
Balance at beginning of period 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]
Net income	485.8
Cash dividends declared	(240.9)
Balance (in shares) at Jun. 30, 2019		353.0			32.2
Balance at end of period at Jun. 30, 2019	7,955.2	$ 3.5	4,960.7	4,987.9	$ (2,003.1)	3.9	2.3
Balance (in shares) at Mar. 31, 2019		352.8			31.1
Balance at beginning of period at Mar. 31, 2019	7,922.6	$ 3.5	4,944.6	4,857.5	$ (1,910.9)	24.8	3.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	250.9			251.5			(0.6)
Other comprehensive income	(20.9)					(20.9)
Cash dividends declared	(120.2)			(120.2)
Issuances of common stock (in shares)		0.2
Issuances of common stock	6.0		6.3		$ (0.3)
Stock-based compensation	8.9		9.8	(0.9)
Purchase of common stock for treasury (in shares)					(1.1)
Purchase of common stock for treasury	(91.9)				$ (91.9)
Distributions paid	(0.2)						(0.2)
Balance (in shares) at Jun. 30, 2019		353.0			32.2
Balance at end of period at Jun. 30, 2019	$ 7,955.2	$ 3.5	$ 4,960.7	$ 4,987.9	$ (2,003.1)	$ 3.9	$ 2.3