Debt

The following table summarizes the carrying value of our outstanding debt:



	Coupon		Carrying Value as of		Effective		Carrying Value as of		Effective
	Rate		December 31, 2015		Interest Rate		December 31, 2014		Interest Rate
	(In millions, except percentages)
Long-Term Debt
Floating Rate Notes:
Senior notes due 2017	LIBOR plus 0.20%		$	450	0.586	%	$	450	0.560	%
Senior notes due 2019	LIBOR plus 0.48%		400		0.825	%	400		0.811	%

Fixed Rate Notes:
Senior notes due 2017	1.350	%	1,000		1.456	%	1,000		1.456	%
Senior notes due 2019	2.200	%	1,148		2.346	%	1,148		2.346	%
Senior notes due 2020	3.250	%	499		3.389	%	498		3.389	%
Senior notes due 2021	2.875	%	749		2.993	%	749		2.993	%
Senior notes due 2022	2.600	%	999		2.678	%	999		2.678	%
Senior notes due 2024	3.450	%	749		3.531	%	749		3.531	%
Senior notes due 2042	4.000	%	744		4.114	%	743		4.114	%
Total senior notes			6,738				6,736
Hedge accounting fair value adjustments			41				22
Other indebtedness			—				19
Total long-term debt			$	6,779			$	6,777

Short-Term Debt
Senior notes due 2015	0.700	%	—		—	%	250		0.820	%
Senior notes due 2015	1.625	%	—		—	%	600		1.805	%
Total short-term debt			—				850
Total Debt			$	6,779			$	7,627

Senior Notes

During the year ended December 31, 2015, $250 million aggregate principal amount of 0.700% fixed rate notes due 2015 and $600 million aggregate principal amount of 1.625% fixed rate notes due 2015 matured and were repaid during the year.

The floating rate notes are not redeemable prior to maturity. We may redeem some or all of the fixed rate notes of each series at any time and from time to time prior to their maturity, generally at a make-whole redemption price.

To help achieve our interest rate risk management objectives, in connection with the previous issuance of certain senior notes, we entered into interest rate swap agreements that effectively converted $2.4 billion of our fixed rate debt to floating rate debt based on LIBOR plus a spread. These swaps were designated as fair value hedges against changes in the fair value of certain fixed rate senior notes resulting from changes in interest rates. The gains and losses related to changes in the fair value of interest rate swaps substantially offset changes in the fair value of the hedged portion of the underlying debt that are attributable to changes in market interest rates.

The effective interest rates for our senior notes include the interest payable, the amortization of debt issuance costs and the amortization of any original issue discount on these senior notes. Interest on these senior notes is payable either quarterly or semiannually. Interest expense associated with these senior notes, including amortization of debt issuance costs, during the years ended December 31, 2015 and 2014 was approximately $178 million and $137 million, respectively. At December 31, 2015, the estimated fair value of these senior notes was approximately $6.5 billion.

The indenture pursuant to which the senior notes were issued includes customary covenants that, among other things and subject to exceptions, limit our ability to incur, assume or guarantee debt secured by liens on specified assets or enter into sale and lease-back transactions with respect to specified properties, and also includes customary events of default.

Commercial Paper

In connection with entering into the credit agreement described below, in November 2015, the Company reduced the aggregate principal amount at maturity of commercial paper notes which may be outstanding under its commercial paper program at any time from $2.0 billion to $1.5 billion to correspond with the $1.5 billion of available borrowing capacity it maintains under the credit agreement for the repayment of commercial paper borrowings in the event it is unable to repay those borrowings from other sources when they become due. We have a $1.5 billion commercial paper program pursuant to which we may issue commercial paper notes with maturities of up to 397 days from the date of issue in an aggregate principal amount of up to $1.5 billion at any time outstanding. As of December 31, 2015, there were no commercial paper notes outstanding.

Credit Agreement

In November 2015, we entered into a credit agreement that provides for an unsecured $2 billion five-year revolving credit facility. We may also, subject to the agreement of the applicable lenders, increase the commitments under the revolving credit facility by up to an aggregate amount of $1 billion. Funds borrowed under the credit agreement may be used for working capital, capital expenditures, acquisitions and other general corporate purposes. The credit agreement replaced our prior $3.0 billion unsecured revolving credit agreement, dated as of November 2011.

As of December 31, 2015, no borrowings were outstanding under our $2 billion credit agreement. However, as described above, we have an up to $1.5 billion commercial paper program and therefore maintain $1.5 billion of available borrowing capacity under our credit agreement in order to repay commercial paper borrowings in the event we are unable to repay those borrowings from other sources when they become due. As a result, at December 31, 2015, $500 million of borrowing capacity was available for other purposes permitted by the credit agreement.

Loans under the credit agreement bear interest at either (i) the London Interbank Offered Rate (“LIBOR”) plus a margin (based on our public debt credit ratings) ranging from 0.875 percent to 1.5 percent or (ii) a formula based on the agent bank's prime rate, the federal funds effective rate plus 0.5 percent or LIBOR plus 1.0 percent, plus a margin (based on our public debt credit ratings) ranging from 0.0 percent to 0.5 percent. The credit agreement will terminate and all amounts owing thereunder will be due and payable on November 9, 2020, unless (a) the commitments are terminated earlier, either at our request or, if an event of default occurs, by the lenders (or automatically in the case of certain bankruptcy-related events of default), or (b) the maturity date is extended upon our request, subject to the agreement of the lenders. The credit agreement contains customary representations, warranties, affirmative and negative covenants, including financial covenants, events of default and indemnification provisions in favor of the banks. The negative covenants include restrictions regarding the incurrence of liens and subsidiary indebtedness, in each case, subject to certain exceptions. The financial covenants require us to meet a quarterly financial test with respect to a minimum consolidated interest coverage ratio and a maximum consolidated leverage ratio.

We were in compliance with all covenants in our outstanding debt instruments for the period ended December 31, 2015.

Future Maturities

Expected future principal maturities as of December 31, 2015 are as follows (in millions):



Fiscal Years:
	2016	$	—
	2017	1,450
	2018	—
	2019	1,550
	2020	500
	Thereafter	3,250
		$	6,750