8. Indebtedness and Derivative Financial Instruments

Our mortgages and unsecured indebtedness, excluding the impact of derivative instruments, consist of the following as of December 31:

	2015		2014
Fixed-Rate Debt:
Mortgage notes, including $44,594 and $49,723 net premiums, respectively. Weighted average interest and maturity of 5.12% and 4.6 years at December 31, 2015.	$	5,985,427	$	5,615,351
Unsecured notes, including $44,698 and $40,701 net discounts, respectively. Weighted average interest and maturity of 3.93% and 7.3 years at December 31, 2015.		13,530,427		13,399,920
Commercial Paper (see below)		878,657		409,185

Total Fixed-Rate Debt		20,394,511		19,424,456
Variable-Rate Debt:
Mortgages notes, at face value. Weighted average interest and maturity of 2.29% and 1.3 years at December 31, 2015.		630,000		630,000
Unsecured Term Loan (see below)		240,000		240,000
Credit Facility (see below)		1,237,662		558,537
Total Variable-Rate Debt		2,107,662		1,428,537

Total Mortgages and Unsecured Indebtedness	$	22,502,173	$	20,852,993

General. 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 December 31, 2015, we were in compliance with all covenants of our unsecured debt.

At December 31, 2015, we or our subsidiaries were the borrowers under 44 non-recourse mortgage notes secured by mortgages on 49 properties, including four separate pools of cross-defaulted and cross-collateralized mortgages encumbering a total of 11 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 applicable borrower under these non-recourse mortgage notes fails to comply with these covenants, the lender could accelerate the debt and enforce its right against their collateral. At December 31, 2015, 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, liquidity or results of operations.

Unsecured Debt

At December 31, 2015, our unsecured debt consisted of $13.5 billion of senior unsecured notes of the Operating Partnership, net of discounts, $1.2 billion outstanding under the Operating Partnership's $4.0 billion unsecured revolving credit facility, or Credit Facility, $240.0 million outstanding under an unsecured term loan, and $878.7 million outstanding under the Operating Partnership's global unsecured commercial paper note program, or Commercial Paper program. The December 31, 2015 balance on the Credit Facility included $237.8 million (U.S. dollar equivalent) of Euro-denominated borrowings and $184.8 million (U.S. dollar equivalent) of Yen-denominated borrowings. At December 31, 2015 the outstanding amount under the Commercial Paper program was $878.7 million, of which $188.1 million was related to the U.S. dollar equivalent of Euro-denominated notes. Foreign currency denominated borrowings under both the Credit Facility and Commercial Paper program are designated as net investment hedges of a portion of our international investments.

On December 31, 2015, we had an aggregate available borrowing capacity of $4.6 billion under the Credit Facility and the Operating Partnership's $2.75 billion supplemental unsecured revolving credit facility, or Supplemental Facility, and together with the Credit Facility, the Credit Facilities. The maximum aggregate outstanding balance under the two Credit Facilities during the year ended December 31, 2015 was $1.8 billion and the weighted average outstanding balance was $1.2 billion. Letters of credit of $36.9 million were outstanding under the two Credit Facilities as of December 31, 2015.

The Credit Facility's initial borrowing capacity of $4.0 billion may be increased to $5.0 billion during its term and provides for borrowings denominated in U.S. dollars, Euros, Yen, Sterling, Canadian dollars and Australian dollars. Borrowings in currencies other than the U.S. dollar are limited to 75% of the maximum revolving credit amount, as defined. The initial maturity date of the Credit Facility is June 30, 2018 and can be extended for an additional year to June 30, 2019 at our sole option, subject to our continued compliance with the terms thereof. The base interest rate on the Credit Facility is LIBOR plus 80 basis points with an additional facility fee of 10 basis points.

On March 2, 2015, the Operating Partnership amended and extended the Supplemental Facility. The initial borrowing capacity of $2.0 billion was increased to $2.75 billion, may be further increased to $3.5 billion during its term, will initially mature on June 30, 2019 and can be extended for an additional year to June 30, 2020 at our sole option, subject to our continued compliance with the terms thereof. The base interest rate on the amended Supplemental Facility was reduced to LIBOR plus 80 basis points and the additional facility fee was reduced to 10 basis points. The Supplemental Facility provides for borrowings denominated in U.S. dollars, Euros, Yen, Sterling, Canadian dollars and Australian dollars.

On March 2, 2015, the Operating Partnership increased the maximum aggregate program size of its Commercial Paper program from $500.0 million to $1.0 billion, or the non-U.S. dollar equivalent thereof. The Operating Partnership may issue unsecured commercial paper notes, denominated in U.S. dollars, Euros and other currencies. Notes issued in non-U.S. currencies may be issued by one or more subsidiaries of the Operating Partnership and are guaranteed by the Operating Partnership. Notes will be sold under customary terms in the U.S. and Euro commercial paper note markets and rank (either by themselves or as a result of the guarantee described above) pari passu with the Operating Partnership's other unsecured senior indebtedness. The Commercial Paper program is supported by the Credit Facilities and if necessary or appropriate, we may make one or more draws under either of the Credit Facilities to pay amounts outstanding from time to time on the Commercial Paper program. At December 31, 2015, we had $878.7 million outstanding under the Commercial Paper program, comprised of $690.6 million outstanding in U.S. dollar denominated notes and $188.1 million (U.S. dollar equivalent) of Euro denominated notes with weighted average interest rates of 0.43% and 0.03%, respectively. The borrowings mature on various dates from January 4, 2016 to April 18, 2016 and reduce amounts otherwise available under the Credit Facilities.

On August 17, 2015, the Operating Partnership issued $500.0 million of senior unsecured notes at a fixed interest rate of 2.50% with a maturity date of September 1, 2020 and $600.0 million of senior unsecured notes at a fixed interest rate of 3.50% with a maturity date of September 1, 2025. Proceeds from the unsecured notes offering were used to repay debt and for general corporate purposes.

On November 18, 2015, a wholly-owned subsidiary of the Operating Partnership issued €750.0 million ($798.3 million U.S. dollar equivalent) of senior unsecured notes at a fixed interest rate of 1.38% with a maturity date of November 18, 2022. Proceeds from the unsecured notes offering were used to pay down a portion of Euro-denominated borrowings on the Credit Facility.

During 2015, we redeemed at par or repaid at maturity $693.5 million of senior unsecured notes with fixed interest rates ranging from 5.10% to 5.75% and completed the early redemption of two series of senior unsecured notes comprising $1.0 billion with fixed interest rates of 6.13% and 7.38%. We recorded a $121.0 million loss on extinguishment of debt in the fourth quarter of 2015 as a result of the early redemption. Further, on February 1, 2016, we redeemed at par $163.3 million of senior unsecured notes with a fixed interest rate of 6.10%.

On January 13, 2016, the Operating Partnership issued $550.0 million of senior unsecured notes at a fixed interest rate of 2.50% with a maturity date of July 15, 2021 and $800.0 million of senior unsecured notes at a fixed interest rate of 3.30% with a maturity date of January 15, 2026. Proceeds from the unsecured notes offering were used to pay down the Credit Facility, unencumber three assets and redeem senior unsecured notes at par in February 2016 and for general corporate purposes.

Mortgage Debt

Total mortgage indebtedness was $6.6 billion and $6.2 billion at December 31, 2015 and 2014, respectively.

During the year ended December 31, 2015, we repaid $259.3 million in mortgage loans, with a weighted average interest rate of 5.51%, unencumbering five properties.

On January 15, 2015, we acquired two properties — Jersey Gardens in Elizabeth, New Jersey (renamed The Mills at Jersey Gardens) and University Park Village in Fort Worth, Texas, subject to existing fixed-rate mortgage loans of $350.0 million and $55.0 million, respectively. The loans mature on November 1, 2020 and May 1, 2028 and bear interest at 3.83% and 3.85%, respectively.

Debt Maturity and Other

Our scheduled principal repayments on indebtedness as of December 31, 2015 are as follows:

2016	$	2,928,580
2017		3,043,067
2018		1,024,275
2019		2,607,519
2020		3,159,632
Thereafter		9,739,204

Total principal maturities		22,502,277
Net unamortized debt discount		(104	)

Total mortgages and unsecured indebtedness	$	22,502,173

Our cash paid for interest in each period, net of any amounts capitalized, was as follows:

	For the Year Ended December 31,
	2015		2014		2013
Cash paid for interest	$	943,683	$	1,018,911	$	1,086,128

Derivative Financial Instruments

Our exposure to market risk due to changes in interest rates primarily relates to our long-term debt obligations. We manage exposure to interest rate market risk through our risk management strategy by a combination of interest rate protection agreements to effectively fix or cap a portion of variable rate debt. We are also exposed to foreign currency risk on financings of certain foreign operations. Our intent is to offset gains and losses that occur on the underlying exposures, with gains and losses on the derivative contracts hedging these exposures. We do not enter into either interest rate protection or foreign currency rate protection agreements for speculative purposes.

We may enter into treasury lock agreements as part of an anticipated debt issuance. Upon completion of the debt issuance, the fair value of these instruments is recorded as part of accumulated other comprehensive income (loss) and is amortized to interest expense over the life of the debt agreement.

The unamortized loss on our treasury locks and terminated hedges recorded in accumulated other comprehensive income (loss) was $60.8 million and $65.7 million as of December 31, 2015 and 2014, respectively. As of December 31, 2015, we had no outstanding interest rate derivatives. As of December 31, 2014, our outstanding LIBOR based derivative contracts consisted of fixed rate swap agreements with a notional amount of $375.0 million.

Within the next year, we expect to reclassify to earnings approximately $12.4 million of losses related to terminated interest rate swaps from the current balance held in accumulated other comprehensive income (loss).

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 including Commercial Paper was $20.4 billion and $19.4 billion as of December 31, 2015 and 2014, respectively. The fair values of these financial instruments and the related discount rate assumptions as of December 31 are summarized as follows:

	2015			2014
Fair value of fixed-rate mortgages and unsecured indebtedness (in millions)	$	21,331		$	20,967
Weighted average discount rates assumed in calculation of fair value for fixed-rate mortgages		3.46	%		3.02	%
Weighted average discount rates assumed in calculation of fair value for unsecured indebtedness		3.59	%		3.51	%