Consolidated Statements of Stockholders' Equity - USD ($) $ in Millions	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated other comprehensive (loss) income
Balance at beginning of year at Dec. 31, 2018		$ 5.7	$ 0.2	$ 2,341.6	$ (44.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock options exercised		0.0	58.5
Purchases of common stock			0.0
Stock-based compensation			5.7
Net earnings	$ 790.9			790.9
Dividends paid in cash				(498.6)
Other comprehensive (loss) income					6.4
Balance at end of year at Dec. 31, 2019	$ 2,665.6	5.7	64.4	2,633.9	(38.4)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends paid per share of common stock (in dollars per share)	$ 0.87
Stock options exercised		0.0	41.0
Purchases of common stock			(52.0)
Stock-based compensation			5.7
Net earnings	$ 859.1			859.1
Dividends paid in cash				(803.4)
Other comprehensive (loss) income					17.2
Balance at end of year at Dec. 31, 2020	$ 2,733.2	5.7	59.1	2,689.6	(21.2)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends paid per share of common stock (in dollars per share)	$ 1.40
Stock options exercised		0.1	31.5
Purchases of common stock			0.0
Stock-based compensation			5.6
Net earnings	$ 925.0			925.0
Dividends paid in cash				(643.7)
Other comprehensive (loss) income					(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