The following table summarizes the major components of debt at each balance sheet date (in millions) and provides the maturities and interest rate ranges of each major category as of June 30, 2017:


	June 30, 2017		December 31, 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 1.4% as of June 30, 2017)		253		—
Other letter of credit facilities, maturing through December 2018		—		—
Canadian term loan and revolving credit facility, maturing March 2019 (weighted average effective interest rate of 2.0% as of June 30, 2017 and 2.1% as of December 31, 2016)		171		239
Senior notes maturing through 2045, interest rates ranging from 2.4% to 7.75% (weighted average interest rate of 4.6% as of June 30, 2017 and December 31, 2016)		6,033		6,033
Tax-exempt bonds, maturing through 2045, fixed and variable interest rates ranging from 0.9% to 5.7% (weighted average interest rate of 1.9% as of June 30, 2017 and 1.8% as of December 31, 2016)		2,305		2,304
Capital leases and other, maturing through 2055, interest rates up to 12%		295		308

		9,057		9,310
Current portion of long-term debt		390		417

	$	8,667	$	8,893