Condensed 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 period at Dec. 31, 2019		$ 2.9	$ 67.2	$ 2,633.9	$ (38.4)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock options exercised			38.3
Purchases of common stock			(52.0)
Stock-based compensation			4.3
Net earnings	$ 663.0			663.0
Dividends paid in cash				(430.2)
Other comprehensive (loss) income					(3.4)
Balance at end of period at Sep. 30, 2020	$ 2,885.6	2.9	57.8	2,866.7	(41.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends paid per share of common stock (in dollars per share)	$ 0.75
Balance at beginning of period at Dec. 31, 2019		2.9	67.2	2,633.9	(38.4)
Balance at end of period at Dec. 31, 2020	$ 2,733.2	2.9	61.9	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
Balance at beginning of period at Jun. 30, 2020		2.9	44.4	2,788.6	(52.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock options exercised			12.0
Purchases of common stock			0.0
Stock-based compensation			1.4
Net earnings	$ 221.5			221.5
Dividends paid in cash				(143.4)
Other comprehensive (loss) income					11.1
Balance at end of period at Sep. 30, 2020	$ 2,885.6	2.9	57.8	2,866.7	(41.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends paid per share of common stock (in dollars per share)	$ 0.25
Balance at end of period at Dec. 31, 2020	$ 2,733.2	2.9	61.9	2,689.6	(21.2)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends paid per share of common stock (in dollars per share)	$ 0.25
Stock options exercised			24.4
Purchases of common stock			0.0
Stock-based compensation			4.3
Net earnings	$ 693.8			693.8
Dividends paid in cash				(482.6)
Other comprehensive (loss) income					(8.4)
Balance at end of period at Sep. 30, 2021	$ 2,964.7	2.9	90.6	2,900.8	(29.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends paid per share of common stock (in dollars per share)	$ 0.84
Balance at beginning of period at Jun. 30, 2021		2.9	78.4	2,818.3	(18.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock options exercised			10.8
Purchases of common stock			0.0
Stock-based compensation			1.4
Net earnings	$ 243.5			243.5
Dividends paid in cash				(161.0)
Other comprehensive (loss) income					(10.8)
Balance at end of period at Sep. 30, 2021	$ 2,964.7	$ 2.9	$ 90.6	$ 2,900.8	$ (29.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends paid per share of common stock (in dollars per share)	$ 0.28