Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

Summary of Significant Accounting Policies

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

The following table summarizes the impacts of revisions in the risk-free discount rate applied to our environmental remediation liabilities and recovery assets for the years ended December 31 (in millions) and the risk-free discount rate applied as of December 31:

	2017			2016			2015
Decrease in operating expenses	$	—		$	(2)		$	(2)
Risk-free discount rate applied to environmental remediation liabilities and recovery assets		2.5	%		2.5	%		2.25	%

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 20
Machinery and equipment — including containers	3 to 30
Buildings and improvements	5 to 40
Furniture, fixtures and office equipment	3 to 10

Summary of Equity and Cost Method Investments

The following table summarizes our equity and cost method investments as of December 31 (in millions):

	2017		2016
Equity method investments	$	127	$	173
Cost method investments		142		147
Investments in unconsolidated entities	$	269	$	320

Schedule of Supplemental Cash Flow Information

	2017		2016		2015
Interest, net of capitalized interest	$	380	$	375	$	384
Income taxes		562		442		419