
3.	Debt

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

Debt Classification

As of June 30, 2011, we had $321 million of debt maturing within the next twelve months, including U.S. $144 million under our Canadian credit facility. We have classified $123 million of these borrowings as long-term as of June 30, 2011 based on our intent and ability to refinance these borrowings on a long-term basis.

Net Debt Borrowings

In February 2011, we issued $400 million of 4.60% senior notes due March 2021. The net proceeds from the debt issuance were $396 million. We used a portion of the proceeds to repay $147 million of 7.65% senior notes that matured in March 2011. During the second quarter of 2011, we repaid approximately $77 million of advances outstanding under our Canadian credit facility with available cash.

Revolving Credit and Letter of Credit Facilities

As of June 30, 2011, we had an aggregate committed capacity of $2.5 billion for letters of credit under various credit facilities. In May 2011, we amended and restated our $2.0 billion revolving credit facility as a result of changes in market conditions, which significantly reduced the cost of the facility. We also extended the term through May 2016. Our revolving credit facility is our primary source of letter of credit capacity. Our remaining letter of credit capacity is provided under facilities with terms that extend from June 2013 to June 2015. As of June 30, 2011, we had an aggregate of $1.5 billion of letters of credit outstanding under various credit facilities. Approximately $1.1 billion of these letters of credit have been issued under our revolving credit facility. There were no borrowings under these credit facilities during the first half of 2011.