Debt (Tables)

12 Months Ended

Dec. 31, 2017

Debt

Components of Debt

The following table summarizes the major components of debt as of each balance sheet date (in millions) and provides the maturities and interest rate ranges of each major category as of December 31:

	2017		2016
$2.25 billion revolving credit facility, maturing July 2020 (weighted average interest rate of 1.9% as of December 31, 2016)	$	—	$	426
Commercial paper program (weighted average interest rate of 1.9% as of December 31, 2017)		515		—
Canadian term loan and revolving credit facility, maturing March 2019 (weighted average effective interest rate of 2.5% as of December 31, 2017 and 2.1% as of December 31, 2016)		113		239
Senior notes, maturing through 2045, interest rates ranging from 2.4% to 7.75% (weighted average interest rate of 4.3% as of December 31, 2017 and 4.6% as of December 31, 2016)		6,184		6,033
Tax-exempt bonds, maturing through 2045, fixed and variable interest rates ranging from 1.2% to 5.7% (weighted average interest rate of 2.0% as of December 31, 2017 and 1.8% as of December 31, 2016)		2,352		2,304
Capital leases and other, maturing through 2055, interest rates up to 12%		327		308
		9,491		9,310
Current portion of long-term debt		739		417
	$	8,752	$	8,893

Summary of the most restrictive covenants requirements

Interest coverage ratio	>  2.75 to 1
Total debt to EBITDA	<  3.50 to 1