CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY/(DEFICIT) - USD ($) shares in Millions, $ in Millions	Common Stock	Capital Surplus	Accumulated Deficit	Accumulated Other Comprehensive Loss	Total
Beginning balance at Dec. 31, 2018	$ 4.4	$ 755.6	$ (838.8)	$ (231.0)	$ (309.8)
Beginning balance (shares) at Dec. 31, 2018	441.2
Increase/(Decrease) in Stockholders' Equity [Roll Forward]
Net income			173.1		173.1
Stock-based compensation		13.7			13.7
Common stock dividends and dividend equivalents declared			(87.4)		(87.4)
Repurchase and retirement of common shares	$ (0.1)		(184.9)		(185.0)
Repurchase and retirement of common shares (shares)	(10.2)
Shares issued under stock-based compensation plans		1.8			1.8
Shares issued under stock-based compensation plans (shares)	1.9
Other comprehensive income (Note 11)				19.4	19.4
Ending balance at Mar. 31, 2019	$ 4.3	771.1	(938.0)	(211.6)	(374.2)
Ending balance (shares) at Mar. 31, 2019	432.9
Beginning balance at Dec. 31, 2018	$ 4.4	755.6	(838.8)	(231.0)	(309.8)
Beginning balance (shares) at Dec. 31, 2018	441.2
Increase/(Decrease) in Stockholders' Equity [Roll Forward]
Net income					787.9
Other comprehensive income (Note 11)					25.3
Ending balance at Jun. 30, 2019	$ 4.3	801.3	(569.7)	(205.7)	30.2
Ending balance (shares) at Jun. 30, 2019	425.9
Beginning balance at Mar. 31, 2019	$ 4.3	771.1	(938.0)	(211.6)	(374.2)
Beginning balance (shares) at Mar. 31, 2019	432.9
Increase/(Decrease) in Stockholders' Equity [Roll Forward]
Net income			614.8		614.8
Stock-based compensation		11.6			11.6
Common stock dividends and dividend equivalents declared			(85.5)		(85.5)
Repurchase and retirement of common shares			(161.0)		(161.0)
Repurchase and retirement of common shares (shares)	(8.3)
Shares issued under stock-based compensation plans		18.6			18.6
Shares issued under stock-based compensation plans (shares)	1.3
Other comprehensive income (Note 11)				5.9	5.9
Ending balance at Jun. 30, 2019	$ 4.3	801.3	(569.7)	(205.7)	30.2
Ending balance (shares) at Jun. 30, 2019	425.9
Beginning balance at Dec. 31, 2019	$ 4.2	841.2	(675.9)	(209.0)	$ (39.5)
Beginning balance (shares) at Dec. 31, 2019	418.0				418.0
Increase/(Decrease) in Stockholders' Equity [Roll Forward]
Net income			176.7		$ 176.7
Stock-based compensation		12.5			12.5
Common stock dividends and dividend equivalents declared			(93.3)		(93.3)
Repurchase and retirement of common shares	$ (0.1)		(235.1)		(235.2)
Repurchase and retirement of common shares (shares)	(9.2)
Shares issued under stock-based compensation plans		1.0			1.0
Shares issued under stock-based compensation plans (shares)	2.1
Other comprehensive income (Note 11)				28.7	28.7
Ending balance at Mar. 31, 2020	$ 4.1	854.7	(828.2)	(180.3)	(149.7)
Ending balance (shares) at Mar. 31, 2020	410.9
Beginning balance at Dec. 31, 2019	$ 4.2	841.2	(675.9)	(209.0)	$ (39.5)
Beginning balance (shares) at Dec. 31, 2019	418.0				418.0
Increase/(Decrease) in Stockholders' Equity [Roll Forward]
Net income					$ 338.6
Other comprehensive income (Note 11)					31.2
Ending balance at Jun. 30, 2020	$ 4.1	860.5	(760.2)	(177.8)	$ (73.4)
Ending balance (shares) at Jun. 30, 2020	411.0				411.0
Increase/(Decrease) in Stockholders' Equity [Roll Forward]
Adoption of new accounting pronouncements (Note 1)			(0.6)		$ (0.6)
Beginning balance at Mar. 31, 2020	$ 4.1	854.7	(828.2)	(180.3)	(149.7)
Beginning balance (shares) at Mar. 31, 2020	410.9
Increase/(Decrease) in Stockholders' Equity [Roll Forward]
Net income			161.9		161.9
Stock-based compensation		5.3			5.3
Common stock dividends and dividend equivalents declared			(93.3)		(93.3)
Repurchase and retirement of common shares			(0.6)		(0.6)
Repurchase and retirement of common shares (shares)	(0.1)
Shares issued under stock-based compensation plans		0.5			0.5
Shares issued under stock-based compensation plans (shares)	0.2
Other comprehensive income (Note 11)				2.5	2.5
Ending balance at Jun. 30, 2020	$ 4.1	$ 860.5	$ (760.2)	$ (177.8)	$ (73.4)
Ending balance (shares) at Jun. 30, 2020	411.0				411.0