Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2021

Summary of Significant Accounting Policies

Accounts Receivable, Allowance for Credit Loss [Table Text Block]

The following table reflects the activity in our allowance for doubtful accounts of trade receivables for the year ended December 31 (in millions):

	2021		2020
Balance as of January 1,	$	33	$	28
Adoption of new accounting standard		—		(1)
Additions charged to expense		35		51
Accounts written-off, net of recoveries		(36)		(44)
Acquisitions, divestitures and other, net		(7)		(1)
Balance as of December 31,	$	25	$	33

Summary of the impact of revisions in risk-free discount rate

	2021			2020			2019
Increase (decrease) in operating expenses	$	(4)		$	8		$	9
Risk-free discount rate applied to environmental remediation liabilities and recovery assets		1.50	%		1.00	%		1.75	%

Schedule of estimated useful lives

The estimated useful lives for significant property and equipment categories are as follows (in years):

	Useful Lives
Vehicles — excluding rail haul cars	3 to 10
Vehicles — rail haul cars	10 to 30
Machinery and equipment — including containers	3 to 30
Buildings and improvements	5 to 40
Furniture, fixtures and office equipment	3 to 10

Summary of investments in unconsolidated entities

	2021		2020
Equity method investments	$	335	$	314
Investments without readily determinable fair values		48		63
Redeemable preferred stock		49		49
Investments in unconsolidated entities	$	432	$	426

Schedule of Supplemental Cash Flow Information

The following table shows supplemental cash flow information for the year ended December 31 (in millions):

	2021		2020		2019
Interest, net of capitalized interest	$	387	$	461	$	397
Income taxes		370		422		292