Consolidated Statements of Stockholders' Equity - USD ($) $ in Millions	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Balance (in shares) at Dec. 31, 2015		289,600,000
Balance at Dec. 31, 2015	$ 1,801.4	$ 2.9	$ 2.0	$ 1,842.9	$ (46.4)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends paid in cash	(346.6)			(346.6)
Purchases of common stock (in shares)		(1,600,000)
Purchases of common stock	(59.5)	$ 0.0	(3.9)	(55.6)
Stock options exercised (in shares)		1,200,000
Stock options exercised	29.3	$ 0.0	29.3
Stock-based compensation	4.1		4.1
Excess tax benefits from stock-based compensation	5.9		5.9
Net earnings	499.4			499.4
Other comprehensive income (loss)	(0.9)				(0.9)
Balance (in shares) at Dec. 31, 2016		289,200,000
Balance at Dec. 31, 2016	1,933.1	$ 2.9	37.4	1,940.1	(47.3)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends paid in cash	(369.1)			(369.1)
Purchases of common stock (in shares)		(1,900,000)
Purchases of common stock	(82.6)	$ 0.0	(43.6)	(39.0)
Stock options exercised (in shares)		300,000
Stock options exercised	9.5	$ 0.0	9.5
Stock-based compensation	5.2		5.2
Net earnings	578.6			578.6
Other comprehensive income (loss)	$ 22.2				22.2
Balance (in shares) at Dec. 31, 2017	287,591,536	287,600,000
Balance at Dec. 31, 2017	$ 2,096.9	$ 2.9	8.5	2,110.6	(25.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends paid in cash	(441.9)			(441.9)
Purchases of common stock (in shares)		(2,000,000)
Purchases of common stock	(103.0)	$ 0.0	(24.0)	(79.0)
Stock options exercised (in shares)		300,000
Stock options exercised	13.4	$ 0.0	13.4
Stock-based compensation	5.1		5.1
Net earnings	751.9			751.9
Other comprehensive income (loss)	$ (19.7)				(19.7)
Balance (in shares) at Dec. 31, 2018	285,901,919	285,900,000
Balance at Dec. 31, 2018	$ 2,302.7	$ 2.9	$ 3.0	$ 2,341.6	$ (44.8)