6. Debt

Unsecured Debt

At September 30, 2013, our unsecured debt consisted of $12.9 billion of senior unsecured notes of the Operating Partnership, $1.2 billion outstanding under our $4.0 billion unsecured revolving credit facility, or Credit Facility, $227.6 million outstanding under our $2.0 billion supplemental unsecured revolving credit facility, or Supplemental Facility, and $240.0 million outstanding under an unsecured term loan. The entire balance on the Credit Facility at September 30, 2013 consisted of Euro-denominated borrowings and the entire balance on the Supplemental Facility on such date consisted of Yen-denominated borrowings, both of which are designated as net investment hedges of our international investments.

On September 30, 2013, we had an aggregate available borrowing capacity of $4.5 billion under the two credit facilities. The maximum outstanding balance of the credit facilities during the nine months ended September 30, 2013 was $1.6 billion and the weighted average outstanding balance was $1.4 billion. Letters of credit of $45.0 million were outstanding under the two credit facilities as of September 30, 2013.

The Credit Facility's initial borrowing capacity of $4.0 billion can be increased at our sole option to $5.0 billion during its term. The Credit Facility will initially mature on October 30, 2015 and can be extended for an additional year at our sole option. As of September 30, 2013, the base interest rate on the Credit Facility was LIBOR plus 95 basis points (reflects a five basis point reduction effective May 16, 2013) with an additional facility fee of 15 basis points. In addition, the Credit Facility provides for a money market competitive bid option program that allows us to hold auctions to achieve lower pricing for short-term borrowings. The Credit Facility also includes a $2.0 billion multi-currency tranche.

The Supplemental Facility's borrowing capacity of $2.0 billion can be increased at our sole option to $2.5 billion during its term. The Supplemental Facility will initially mature on June 30, 2016 and can be extended for an additional year at our sole option. As of September 30, 2013, the base interest rate on the Supplemental Facility was LIBOR plus 95 basis points (reflects a five basis point reduction effective May 16, 2013) with an additional facility fee of 15 basis points. Like the Credit Facility, the Supplemental Facility provides for a money market competitive bid option program and allows for multi-currency borrowings.

During the nine months ended September 30, 2013, we redeemed at par or repaid at maturity $504.5 million of senior unsecured notes with fixed rates ranging from 5.30% to 7.18% with cash on hand. In addition, we repaid a $240.0 million mortgage loan with the proceeds from a $240.0 million unsecured term loan. The term loan has a capacity of up to $300.0 million, bears interest at LIBOR plus 110 basis points and matures on February 28, 2016 with two available one-year extension options.

On October 2, 2013, the Operating Partnership issued €750.0 million ($1.0 billion USD equivalent) of senior unsecured notes at a fixed interest rate of 2.375% with a maturity date of October 2, 2020. Proceeds from the unsecured notes offering were used to pay down a portion of Euro-denominated borrowings on the Credit Facility and the acquisition of various assets in the McArthurGlen transactions further discussed in Note 5. These notes are designated as a net investment hedge of our Euro-denominated international investments.

Mortgage Debt

Total mortgage indebtedness was $8.1 billion and $8.0 billion at September 30, 2013 and December 31, 2012, respectively.

Covenants

Our unsecured debt agreements contain financial covenants and other non-financial covenants. If we were to fail to comply with these covenants, after the expiration of the applicable cure periods, the debt maturity could be accelerated or other remedies could be sought by the lender including adjustments to the applicable interest rate. As of September 30, 2013, we were in compliance with all covenants of our unsecured debt.

At September 30, 2013, we or our subsidiaries are the borrowers under 79 non-recourse mortgage notes secured by mortgages on 79 properties, including seven separate pools of cross-defaulted and cross-collateralized mortgages encumbering a total of 27 properties. Under these cross-default provisions, a default under any mortgage included in the cross-defaulted pool may constitute a default under all mortgages within that pool and may lead to acceleration of the indebtedness due on each property within the pool. Certain of our secured debt instruments contain financial and other non-financial covenants which are specific to the properties which serve as collateral for that debt. If the borrower fails to comply with these covenants, the lender could accelerate the debt and enforce its right against their collateral. At September 30, 2013, the applicable borrowers under these non-recourse mortgage notes were in compliance with all covenants where non-compliance could individually, or giving effect to applicable cross-default provisions in the aggregate, have a material adverse effect on our financial condition, results of operations or cash flows.

Fair Value of Debt

The carrying value of our variable-rate mortgages and other loans approximates their fair values. We estimate the fair values of consolidated fixed-rate mortgages using cash flows discounted at current borrowing rates and other indebtedness using cash flows discounted at current market rates. We estimate the fair values of consolidated fixed-rate unsecured notes using quoted market prices, or, if no quoted market prices are available, we use quoted market prices for securities with similar terms and maturities. The book value of our consolidated fixed-rate mortgages and unsecured indebtedness was $20.7 billion and $21.0 billion as of September 30, 2013 and December 31, 2012, respectively. The fair values of these financial instruments and the related discount rate assumptions as of September 30, 2013 and December 31, 2012 are summarized as follows:

	September 30, 2013		December 31, 2012

Fair value of fixed-rate mortgages and unsecured indebtedness	$	22,140	$	23,373
Weighted average discount rates assumed in calculation of fair value for fixed-rate mortgages		3.55%		3.24%