Consolidated Statements Of Changes In Equity - USD ($) shares in Millions, $ in Millions	Total	Common shares	Capital contribution reserve	Retained earnings	Accumulated other comprehensive income (loss)
Balance (in shares) at Dec. 31, 2018		171.4
Beginning Balance at Dec. 31, 2018	$ 1,836.1	$ 1.7	$ 1,893.8	$ 169.2	$ (228.6)
Net income	355.7			355.7
Other comprehensive loss, net of tax	2.1				2.1
Dividends declared	(123.9)			(123.9)
Share repurchase (in shares)		(4.0)
Share repurchases	$ (150.0)	$ 0.0	(150.0)
Exercise of options, net of shares tendered for payment (in shares)	0.7
Exercise of options, net of shares tendered for payment	$ 17.1		17.1
Issuance of restricted shares, net of cancellations (in shares)	0.3
Issuance of restricted shares, net of cancellations	$ 0.0
Shares surrendered by employees to pay taxes (in shares)		(0.1)
Shares surrendered by employees to pay taxes	(4.6)		(4.6)
Share-based compensation	21.4		21.4
Balance (in shares) at Dec. 31, 2019		168.3
Ending Balance at Dec. 31, 2019	1,953.9	$ 1.7	1,777.7	401.0	(226.5)
Net income	358.6			358.6
Other comprehensive loss, net of tax	19.2				19.2
Dividends declared	(128.4)			(128.4)
Share repurchase (in shares)		(3.7)
Share repurchases	(150.2)		(150.2)
Exercise of options, net of shares tendered for payment (in shares)		1.3
Exercise of options, net of shares tendered for payment	37.6		37.6
Issuance of restricted shares, net of cancellations (in shares)		0.3
Issuance of restricted shares, net of cancellations	0.0
Shares surrendered by employees to pay taxes (in shares)		(0.1)
Shares surrendered by employees to pay taxes	(4.7)		(4.7)
Share-based compensation	20.3		20.3
Balance (in shares) at Dec. 31, 2020		166.1
Ending Balance at Dec. 31, 2020	2,106.3	$ 1.7	1,680.7	631.2	(207.3)
Net income	553.0			553.0
Other comprehensive loss, net of tax	(6.6)				(6.6)
Dividends declared	(132.8)			(132.8)
Share repurchase (in shares)		(2.1)
Share repurchases	$ (150.0)		(150.0)
Exercise of options, net of shares tendered for payment (in shares)	0.9	0.9
Exercise of options, net of shares tendered for payment	$ 30.1		30.1
Issuance of restricted shares, net of cancellations (in shares)		0.3
Issuance of restricted shares, net of cancellations	0.0
Shares surrendered by employees to pay taxes (in shares)		(0.1)
Shares surrendered by employees to pay taxes	(7.9)		(7.9)
Share-based compensation	29.8		29.8
Balance (in shares) at Dec. 31, 2021		165.1
Ending Balance at Dec. 31, 2021	$ 2,421.9	$ 1.7	$ 1,582.7	$ 1,051.4	$ (213.9)