Consolidated Balance Sheets (Parenthetical) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Marketable debt securities, allowance	$ 0	$ 0
Preferred stock, no par value	$ 0	$ 0
Preferred stock, authorized	1,000,000.0	1,000,000.0
Preferred stock, issued	0	0
Common stock, par value	$ 1	$ 1
Common stock, authorized	1,200,000,000	1,200,000,000
Common stock, issued	346,600,000	346,300,000
Truck, Parts and Other
Allowance for losses	$ 600,000	$ 600,000
Marketable debt securities, amortized cost	1,409,700,000	1,154,000,000.0
Marketable debt securities, allowance	0	0
Financial Services
Allowance for credit losses	$ 127,000,000.0	$ 112,400,000