Unaudited Condensed Consolidated Statement Of Shareholders' Equity - USD ($) $ in Millions	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Treasury Stock
BALANCE at period start (in shares) at Dec. 31, 2020		102,562,149
BALANCE at period start at Dec. 31, 2020	$ 3,235.7	$ 1.0	$ 53.1	$ 4,069.4	$ (887.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	239.4			239.4
Repurchases of common stock	(306.1)				(306.1)
Stock-based compensation expense	20.8		20.8
Shares awarded under stock-based compensation plans, net of shares withheld for taxes	4.1		(32.9)		37.0
BALANCE at period end (in shares) at Mar. 31, 2021		102,562,149
BALANCE at period end at Mar. 31, 2021	3,193.9	$ 1.0	41.0	4,308.8	(1,156.9)
BALANCE at period start (in shares) at Dec. 31, 2020		102,562,149
BALANCE at period start at Dec. 31, 2020	3,235.7	$ 1.0	53.1	4,069.4	(887.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	985.9
BALANCE at period end (in shares) at Sep. 30, 2021		86,562,149
BALANCE at period end at Sep. 30, 2021	2,356.5	$ 0.8	1.6	4,258.1	(1,904.0)
BALANCE at period start (in shares) at Mar. 31, 2021		102,562,149
BALANCE at period start at Mar. 31, 2021	3,193.9	$ 1.0	41.0	4,308.8	(1,156.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	384.8			384.8
Repurchases of common stock	(736.1)				(736.1)
Treasury stock cancellation (in shares)		(16,000,000)
Treasury stock cancellation		$ (0.2)	(40.6)	(797.2)	838.0
Stock-based compensation expense	6.5		6.5
Shares awarded under stock-based compensation plans, net of shares withheld for taxes	7.7		(1.2)		8.9
BALANCE at period end (in shares) at Jun. 30, 2021		86,562,149
BALANCE at period end at Jun. 30, 2021	2,856.8	$ 0.8	5.7	3,896.4	(1,046.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	361.7			361.7
Repurchases of common stock	(879.2)				(879.2)
Stock-based compensation expense	4.3		4.3
Shares awarded under stock-based compensation plans, net of shares withheld for taxes	12.9		(8.4)		21.3
BALANCE at period end (in shares) at Sep. 30, 2021		86,562,149
BALANCE at period end at Sep. 30, 2021	2,356.5	$ 0.8	1.6	4,258.1	(1,904.0)
BALANCE at period start (in shares) at Dec. 31, 2021		86,562,149
BALANCE at period start at Dec. 31, 2021	2,377.0	$ 0.8	3.2	4,639.9	(2,266.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	362.1			362.1
Repurchases of common stock	(380.9)				(380.9)
Stock-based compensation expense	15.9		15.9
Shares awarded under stock-based compensation plans, net of shares withheld for taxes	(28.5)		(16.7)	(58.1)	46.3
BALANCE at period end (in shares) at Mar. 31, 2022		86,562,149
BALANCE at period end at Mar. 31, 2022	2,345.6	$ 0.8	2.4	4,943.9	(2,601.5)
BALANCE at period start (in shares) at Dec. 31, 2021		86,562,149
BALANCE at period start at Dec. 31, 2021	2,377.0	$ 0.8	3.2	4,639.9	(2,266.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	1,091.0
BALANCE at period end (in shares) at Sep. 30, 2022		86,562,149
BALANCE at period end at Sep. 30, 2022	2,255.2	$ 0.8	9.3	5,672.8	(3,427.7)
BALANCE at period start (in shares) at Mar. 31, 2022		86,562,149
BALANCE at period start at Mar. 31, 2022	2,345.6	$ 0.8	2.4	4,943.9	(2,601.5)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	376.3			376.3
Repurchases of common stock	(403.9)				(403.9)
Stock-based compensation expense	5.3		5.3
Shares awarded under stock-based compensation plans, net of shares withheld for taxes	1.7		(2.5)		4.2
BALANCE at period end (in shares) at Jun. 30, 2022		86,562,149
BALANCE at period end at Jun. 30, 2022	2,325.0	$ 0.8	5.2	5,320.2	(3,001.2)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	352.6			352.6
Repurchases of common stock	(428.2)				(428.2)
Stock-based compensation expense	5.1		5.1
Shares awarded under stock-based compensation plans, net of shares withheld for taxes	0.7		(1.0)		1.7
BALANCE at period end (in shares) at Sep. 30, 2022		86,562,149
BALANCE at period end at Sep. 30, 2022	$ 2,255.2	$ 0.8	$ 9.3	$ 5,672.8	$ (3,427.7)