Marketable Securities (Detail) - Truck, Parts and Other - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Schedule Of Available For Sale Securities [Line Items]
Marketable debt securities, Cost	$ 1,671.1
Marketable debt securities, Fair Value	1,613.0
Marketable equity securities, Cost	10.0	$ 15.4
Marketable equity securities, Unrealized Gains		1.3
Marketable equity securities, Unrealized Losses	8.8	3.0
Marketable equity securities, Fair Value	1.2	13.7
Total marketable securities, Cost	1,681.1	1,562.7
Total marketable securities, Unrealized Gains	0.9	6.4
Total marketable securities, Unrealized Losses	67.8	9.7
Total marketable securities, Fair Value	1,614.2	1,559.4
U.S. tax-exempt securities
Schedule Of Available For Sale Securities [Line Items]
Marketable debt securities, Cost	452.8	431.4
Marketable debt securities, Unrealized Gains	0.5	1.5
Marketable debt securities, Unrealized Losses	8.2	0.4
Marketable debt securities, Fair Value	445.1	432.5
U.S. taxable municipal / non-U.S. provincial bonds
Schedule Of Available For Sale Securities [Line Items]
Marketable debt securities, Cost	191.6	192.2
Marketable debt securities, Unrealized Gains		0.6
Marketable debt securities, Unrealized Losses	10.8	1.2
Marketable debt securities, Fair Value	180.8	191.6
U.S. corporate securities
Schedule Of Available For Sale Securities [Line Items]
Marketable debt securities, Cost	262.5	208.3
Marketable debt securities, Unrealized Gains	0.1	0.6
Marketable debt securities, Unrealized Losses	11.6	1.5
Marketable debt securities, Fair Value	251.0	207.4
U.S. government and agency securities
Schedule Of Available For Sale Securities [Line Items]
Marketable debt securities, Cost	118.0	95.9
Marketable debt securities, Unrealized Gains	0.1	0.6
Marketable debt securities, Unrealized Losses	3.1	0.1
Marketable debt securities, Fair Value	115.0	96.4
Non-U.S. corporate securities
Schedule Of Available For Sale Securities [Line Items]
Marketable debt securities, Cost	467.9	443.9
Marketable debt securities, Unrealized Gains		1.4
Marketable debt securities, Unrealized Losses	17.9	2.5
Marketable debt securities, Fair Value	450.0	442.8
Non-U.S. government securities
Schedule Of Available For Sale Securities [Line Items]
Marketable debt securities, Cost	78.9	75.2
Marketable debt securities, Unrealized Gains	0.2	0.1
Marketable debt securities, Unrealized Losses	2.7	0.3
Marketable debt securities, Fair Value	76.4	75.0
Other debt securities
Schedule Of Available For Sale Securities [Line Items]
Marketable debt securities, Cost	99.4	100.4
Marketable debt securities, Unrealized Gains		0.3
Marketable debt securities, Unrealized Losses	4.7	0.7
Marketable debt securities, Fair Value	$ 94.7	$ 100.0

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