Compare Currently Reported Amounts and Reported Under LIFO in Consolidated Statements of Comprehensive Income (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Income taxes	$ 837.1	$ 530.8	$ 360.4
Net income	$ 3,011.6	$ 1,865.5	$ 1,301.2
Net Income Per Share
Basic	$ 5.76	$ 3.58	$ 2.50
Diluted	$ 5.75	$ 3.57	$ 2.50
Truck, Parts and Other
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Cost of sales and revenues	$ 23,291.0	$ 19,092.4	$ 15,072.7
Income taxes	837.1	530.8	360.4
Net income	$ 3,011.6	1,865.5	1,301.2
Net Income Per Share
Basic	$ 5.76
Diluted	$ 5.75
Truck, Parts and Other | Pro Forma Under LIFO
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Cost of sales and revenues	$ 23,340.4
Income taxes	824.9
Net income	$ 2,974.4
Net Income Per Share
Basic	$ 5.69
Diluted	$ 5.68
Truck, Parts and Other | Adjustment
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Cost of sales and revenues	$ (49.4)	(17.7)	(3.7)
Income taxes	12.2	4.3	0.9
Net income	$ 37.2	$ 13.4	$ 2.8
Net Income Per Share
Basic	$ 0.07
Diluted	$ 0.07