Consolidated Statements of Changes in Stockholders' Equity - USD ($) shares in Thousands, $ in Millions	Total	Common Stock	Additional Paid in Capital	Retained Earnings	Accumulated Other Comprehensive Loss
Beginning Balance at Dec. 31, 2020	$ 3,246.3	$ 0.9	$ 554.4	$ 2,835.5	$ (144.5)
Beginning Balance (in shares) at Dec. 31, 2020		94,830
Common stock withheld and retired to cover taxes on vested stock awards	(10.5)	$ (0.1)	(0.6)	(9.8)
Common stock withheld and retired to cover taxes on vested stock awards (in shares)		(77)
Common stock dividends declared	(190.9)			(190.9)
Share-based compensation and other	20.8	$ 0.2	20.7	(0.1)
Share-based compensation expense (in shares)		226
Comprehensive income	378.6			373.8	4.8
Ending Balance at Jun. 30, 2021	3,444.3	$ 1.0	574.5	3,008.5	(139.7)
Ending Balance (in shares) at Jun. 30, 2021		94,979
Beginning Balance at Mar. 31, 2021	3,331.2	$ 1.0	566.0	2,906.3	(142.1)
Beginning Balance (in shares) at Mar. 31, 2021		94,994
Common stock withheld and retired to cover taxes on vested stock awards	(10.4)	$ (0.1)	(0.6)	(9.7)
Common stock withheld and retired to cover taxes on vested stock awards (in shares)		(76)
Common stock dividends declared	(95.4)			(95.4)
Share-based compensation and other	9.2	$ 0.1	9.1
Share-based compensation expense (in shares)		61
Comprehensive income	209.7			207.3	2.4
Ending Balance at Jun. 30, 2021	3,444.3	$ 1.0	574.5	3,008.5	(139.7)
Ending Balance (in shares) at Jun. 30, 2021		94,979
Beginning Balance at Dec. 31, 2021	3,607.2	$ 0.9	579.4	3,102.1	(75.2)
Beginning Balance (in shares) at Dec. 31, 2021		93,539
Common stock withheld and retired to cover taxes on vested stock awards	(9.5)		(0.6)	(8.9)
Common stock withheld and retired to cover taxes on vested stock awards (in shares)		(67)
Common stock dividends declared	(211.9)			(211.9)
Share-based compensation and other	22.2		22.2
Share-based compensation expense (in shares)		214
Comprehensive income	556.5			555.7	0.8
Ending Balance at Jun. 30, 2022	3,964.5	$ 0.9	601.0	3,437.0	(74.4)
Ending Balance (in shares) at Jun. 30, 2022		93,686
Beginning Balance at Mar. 31, 2022	3,779.3	$ 0.9	591.7	3,261.9	(75.2)
Beginning Balance (in shares) at Mar. 31, 2022		93,704
Common stock withheld and retired to cover taxes on vested stock awards	(9.2)	$ 0.0	(0.5)	(8.7)	0.0
Common stock withheld and retired to cover taxes on vested stock awards (in shares)		(66)
Common stock dividends declared	(117.7)	$ 0.0	0.0	(117.7)	0.0
Share-based compensation and other	9.8	$ 0.0	9.8	0.0	0.0
Share-based compensation expense (in shares)		48
Comprehensive income	302.3	$ 0.0	0.0	301.5	0.8
Ending Balance at Jun. 30, 2022	$ 3,964.5	$ 0.9	$ 601.0	$ 3,437.0	$ (74.4)
Ending Balance (in shares) at Jun. 30, 2022		93,686