Consolidated Statements of Stockholders' Equity - USD ($) $ in Millions	Total	Common stock	Additional paid-in capital	Retained earnings	Accumulated other comprehensive income (loss)
Balance at beginning of year at Dec. 31, 2020		$ 5.7	$ 59.1	$ 2,689.6	$ (21.2)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock options exercised		0.1	31.5
Purchases of common stock			0.0	0.0
Stock-based compensation			5.6
Net earnings	$ 925.0			925.0
Cash dividends paid				(643.7)
Translation adjustment upon merger of foreign subsidiary				0.0
Other comprehensive income (loss)					(9.5)
Balance at end of year at Dec. 31, 2021	$ 3,042.2	5.8	96.2	2,970.9	(30.7)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends paid per share of common stock (in dollars per share)	$ 1.12
Stock options exercised		(0.1)	9.3
Purchases of common stock			(109.1)	(128.7)
Stock-based compensation			7.2
Net earnings	$ 1,086.9			1,086.9
Cash dividends paid				(711.3)
Translation adjustment upon merger of foreign subsidiary				0.9
Other comprehensive income (loss)					(34.1)
Balance at end of year at Dec. 31, 2022	$ 3,163.2	5.7	3.6	3,218.7	(64.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends paid per share of common stock (in dollars per share)	$ 1.24
Stock options exercised		0.0	30.1
Purchases of common stock			0.0	0.0
Stock-based compensation			7.3
Net earnings	$ 1,155.0			1,155.0
Cash dividends paid				(1,016.8)
Translation adjustment upon merger of foreign subsidiary				0.0
Other comprehensive income (loss)					10.0
Balance at end of year at Dec. 31, 2023	$ 3,348.8	$ 5.7	$ 41.0	$ 3,356.9	$ (54.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends paid per share of common stock (in dollars per share)	$ 1.78