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 June 30, 2018:


	June 30,		December 31,
	2018		2017
Revolving credit facility	$	—	$	—
Commercial paper program (weighted average interest rate of 2.4% as of June 30, 2018 and 1.9% as of December 31, 2017)		968		515
Canadian term loan and revolving credit facility, maturing March 2019 (weighted average effective interest rate of 2.7% as of June 30, 2018 and 2.5% as of December 31, 2017)		71		113
Senior notes, maturing through 2045, interest rates ranging from 2.4% to 7.75% (weighted average interest rate of 4.3% as of June 30, 2018 and December 31, 2017)		6,222		6,222
Tax-exempt bonds, maturing through 2045, fixed and variable interest rates ranging from 1.35% to 5.7% (weighted average interest rate of 2.2% as of June 30, 2018 and 2.0% as of December 31, 2017)		2,328		2,370
Capital leases and other, maturing through 2040, interest rates up to 12%		260		327
Debt issuance costs, discounts and other		(53)		(56)
		9,796		9,491
Current portion of long-term debt		828		739
	$	8,968	$	8,752