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, 2014:


	March 31, 2014		December 31, 2013
U.S. revolving credit facility, maturing July 2018 (weighted average interest rate of 1.2% at March 31, 2014 and December 31, 2013)	$	790	$	420
Letter of credit facilities, maturing through December 2016		—		—
Canadian credit facility and term loan, maturing November 2017 (weighted average effective interest rate of 2.5% at March 31, 2014 and 2.7% at December 31, 2013)		375		414
Senior notes maturing through 2039, interest rates ranging from 2.60% to 7.75% (weighted average interest rate of 5.8% at March 31, 2014 and 5.7% at December 31, 2013)		5,933		6,287
Tax-exempt bonds, maturing through 2045, fixed and variable interest rates ranging from 0.06% to 5.7% (weighted average interest rate of 2.3% at March 31, 2014 and December 31, 2013)		2,664		2,664
Capital leases and other, maturing through 2055, interest rates up to 12%		432		441

		10,194		10,226
Current portion of long-term debt		1,216		726

	$	8,978	$	9,500