
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 September 30, 2011:


	September 30,		December 31,
	2011		2010

Revolving credit facility	$	—	$	—
Letter of credit facilities		—		—
Canadian credit facility (weighted average effective interest rate of 2.3% at September 30, 2011 and 2.2% at December 31, 2010)		133		212
Senior notes and debentures, maturing through 2039, interest rates ranging from 2.60% to 7.75% (weighted average interest rate of 6.0% at September 30, 2011 and 6.5% at December 31, 2010)		6,233		5,452
Tax-exempt bonds, maturing through 2041, fixed and variable interest rates ranging from 0.2% to 7.4% (weighted average interest rate of 3.0% at September 30, 2011 and 3.1% at December 31, 2010)		2,751		2,696
Tax-exempt project bonds, maturing through 2029, fixed and variable interest rates ranging from 0.2% to 3.4% (weighted average interest rate of 1.4% at September 30, 2011 and 2.5% at December 31, 2010)		86		116
Capital leases and other, maturing through 2050, interest rates up to 12%		410		431

		9,613		8,907
Current portion of long-term debt		225		233

	$	9,388	$	8,674

Debt Classification

As of September 30, 2011, we had $348 million of debt maturing within the next twelve months, including U.S. $133 million under our Canadian credit facility. We have classified $123 million of these borrowings as long-term as of September 30, 2011 based on our intent and ability to refinance these borrowings on a long-term basis.

Debt Borrowings and Repayments

The significant changes in our debt balances from December 31, 2010 to September 30, 2011 are related to the following:

Canadian credit facility — The decrease in the carrying value is primarily due to $77 million of debt repayments during the nine months ended September 30, 2011.

Senior notes — 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. In August 2011, we issued $500 million of 2.60% senior notes due September 2016. The net proceeds from the debt issuance were $497 million. A portion of the proceeds was used to repay the $100 million borrowing under our $2.0 billion revolving credit facility incurred in connection with our acquisition of Oakleaf, which is discussed below.

Tax-exempt bonds — We issued $80 million of tax-exempt bonds during the nine months ended September 30, 2011. The proceeds from the issuance of the bonds were deposited directly into a trust fund and may only be used for the specific purpose for which the money was raised. Accordingly, the restricted funds provided by these financing activities have not been included in “New borrowings” in our Condensed Consolidated Statement of Cash Flows. During the nine months ended September 30, 2011, we repaid $25 million of our tax-exempt bonds with available cash.

Tax-exempt project bonds — We repaid $30 million of tax-exempt project bonds with available cash during the nine months ended September 30, 2011.

Capital leases and other — The decrease in our capital leases and other debt obligations is primarily due to the repayment of various borrowings upon their scheduled maturities.

Revolving Credit and Letter of Credit Facilities

As of September 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 September 30, 2011, we had an aggregate of $1.5 billion of letters of credit outstanding under various credit facilities. Approximately $1.0 billion of these letters of credit have been issued under our revolving credit facility. During the third quarter of 2011, we borrowed $100 million under our revolving credit facility in connection with our acquisition of Oakleaf. These borrowings were repaid with proceeds from our August 2011 issuance of senior notes. See Note 10 for additional information related to this acquisition. There were no outstanding borrowings under these credit facilities as of September 30, 2011.