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:


	2018		2017
Revolving credit facility (weighted average interest rate of 3.1% as of December 31, 2018)	$	11	$	—
Commercial paper program (weighted average interest rate of 2.9% as of December 31, 2018 and 1.9% as of December 31, 2017)		990		515
Canadian term loan and revolving credit facility (weighted average effective interest rate of 2.5% as of December 31, 2017)		—		113
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, 2018 and December 31, 2017)		6,222		6,222
Tax-exempt bonds, maturing through 2048, fixed and variable interest rates ranging from 1.35% to 4.3% (weighted average interest rate of 2.35% as of December 31, 2018 and 2.0% as of December 31, 2017)		2,388		2,370
Capital leases and other, maturing through 2040, interest rates up to 12%		467		327
Debt issuance costs, discounts and other		(52)		(56)
		10,026		9,491
Current portion of long-term debt		432		739
	$	9,594	$	8,752