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 March 31, 2016:


	March 31, 2016		December 31, 2015
$2.25 billion revolving credit facility, maturing July 2020 (weighted average interest rate of 1.4% at March 31, 2016)	$	458	$	20
Letter of credit facilities, maturing through December 2018		—		—
Canadian credit facility and term loan, maturing March 2019 (weighted average effective interest rate of 2.0% at March 31, 2016 and 2.2% at December 31, 2015)		353		84
Senior notes maturing through 2045, interest rates ranging from 2.60% to 7.75% (weighted average interest rate of 4.7% at March 31, 2016 and December 31, 2015)		6,039		6,050
Tax-exempt bonds, maturing through 2045, fixed and variable interest rates ranging from 0.4% to 5.7% (weighted average interest rate of 2.0% at March 31, 2016 and 1.9% at December 31, 2015)		2,418		2,447
Capital leases and other, maturing through 2055, interest rates up to 12%		328		328

		9,596		8,929
Current portion of long-term debt		524		253

	$	9,072	$	8,676