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, 2011 and December 31, 2010:


	June 30,		December 31,
	2011		2010

Revolving credit facility	$	—	$	—
Letter of credit facilities		—		—
Canadian credit facility (weighted average effective interest rate of 2.3% at June 30, 2011 and 2.2% at December 31, 2010)		144		212
Senior notes and debentures, maturing through 2039, interest rates ranging from 4.60% to 7.75% (weighted average interest rate of 6.3% at June 30, 2011 and 6.5% at December 31, 2010)		5,710		5,452
Tax-exempt bonds maturing through 2039, fixed and variable interest rates ranging from 0.1% to 7.4% (weighted average interest rate of 3.1% at June 30, 2011 and December 31, 2010)		2,671		2,696
Tax-exempt project bonds, principal payable in periodic installments, maturing through 2029, fixed and variable interest rates ranging from 0.1% to 3.4% (weighted average interest rate of 1.3% at June 30, 2011 and 2.5% at December 31, 2010)		86		116
Capital leases and other, maturing through 2050, interest rates up to 12%		426		431

		9,037		8,907
Current portion of long-term debt		198		233

	$	8,839	$	8,674