Debt

At December 31, our debt consisted of the following:



	2016			2015
	(In millions)
Senior unsecured debt:
Revolving credit facility — LIBOR based loans (matures in June 2020)	$	—		$	—
Money market lines of credit	—			39
Total credit arrangements	—			39
5¾% Senior Notes due 2022	750			750
5⅝% Senior Notes due 2024	1,000			1,000
5⅜% Senior Notes due 2026	700			700
Total senior unsecured debt	2,450			2,489
Debt issuance costs	(19		)	(22		)
Total long-term debt	$	2,431		$	2,467

Credit Arrangements

In March 2016, we entered into the fifth amendment to our Credit Agreement. This amendment changed certain definitions related to our financial covenants and decreased our interest coverage ratio from 3.0:1.0 to 2.5:1.0. Our borrowing capacity remains at $1.8 billion and the facility maturity date remains June 2020. We incurred approximately $3 million of financing costs related to this amendment, which were included in "Interest expense" on our consolidated statement of operations. As of December 31, 2016, the largest individual loan commitment by any lender was 12% of total commitments.

During 2016, our debt rating was downgraded by rating agencies, and as a result, our borrowing costs under the credit facility increased by 25 basis points. In addition, our available borrowing capacity (before any amounts drawn) under our money market lines of credit with various institutions, the availability of which is at the discretion of those financial institutions, was reduced from $195 million at December 31, 2015 to $125 million at December 31, 2016. This borrowing capacity is subject to compliance with restrictive covenants in our credit facility.

Loans under the credit facility bear interest, at our option, equal to (a) a rate per annum equal to the higher of the prime rate announced from time to time by JPMorgan Chase Bank, N.A. or the weighted average of the rates on overnight federal funds transactions with members of the Federal Reserve System during the last preceding business day plus 50 basis points, plus a margin that is based on a grid of our debt rating (100 basis points per annum at December 31, 2016) or (b) the London Interbank Offered Rate, plus a margin that is based on a grid of our debt rating (200 basis points per annum at December 31, 2016).

Under our credit facility, we pay commitment fees on available but undrawn amounts based on a grid of our debt rating (37.5 basis points per annum at December 31, 2016). We incurred aggregate commitment fees under our credit facility of approximately $7 million, $5 million and $4 million for each of the years ended December 31, 2016, 2015 and 2014, respectively, which were recorded in “Interest expense” on our consolidated statement of operations.

Our credit facility has restrictive financial covenants that include the maintenance of a ratio of total debt to book capitalization not to exceed 0.6 to 1.0 and the maintenance of a ratio of earnings before gain or loss on the disposition of assets, interest expense, income taxes and noncash items (such as depreciation, depletion and amortization expense, unrealized gains and losses on commodity derivatives and ceiling test impairments) to interest expense of at least 2.5 to 1.0. At December 31, 2016, we were in compliance with all of our debt covenants.

As of December 31, 2016, we had no letters of credit outstanding under our credit facility. Letters of credit are subject to a fronting fee of 20 basis points and annual fees based on a grid of our debt rating (200 basis points at December 31, 2016).

The credit facility includes events of default relating to customary matters, including, among other things, nonpayment of principal, interest or other amounts; violation of covenants; inaccuracy of representations and warranties in any material respect when made; a change of control; or certain other material adverse changes in our business. Our senior notes also contain standard events of default. If any of the foregoing defaults were to occur, our lenders under the credit facility could terminate future lending commitments, and our lenders under both the credit facility and our notes could declare the outstanding borrowings due and payable. In addition, our credit facility, senior notes and substantially all of our derivative arrangements contain provisions that provide for cross defaults and acceleration of those debt and derivative instruments in certain situations. See Note 1, "Organization and Summary of Significant Accounting Policies – Concentration of Credit Risk," for additional details.

Senior Notes and Senior Subordinated Notes

In March 2015, we issued $700 million of 5⅜% Senior Notes due 2026 and received net proceeds of $691 million (net of offering costs of approximately $9 million). These notes were issued at par to yield 5⅜%. In April 2015, we redeemed our $700 million aggregate principal amount of 6⅞% Senior Subordinated Notes due 2020. In connection with the redemption, we paid a premium of $24 million. The premium was recorded under the caption "Other income (expense) — Other, net" on our consolidated statement of income. In addition, associated unamortized offering costs and discounts of approximately $8 million were charged to interest expense during the second quarter of 2015 as a result of the redemption.

Interest on our senior notes is payable semi-annually. The notes are unsecured and unsubordinated obligations and rank equally with all of our other existing and future unsecured and unsubordinated obligations. We may redeem some or all of our senior notes at any time before their maturity at a redemption price based on a make-whole amount plus accrued and unpaid interest to the date of redemption. The indentures governing our senior notes contain covenants that may limit our ability to, among other things, incur debt secured by liens; enter into sale/leaseback transactions; and enter into merger or consolidation transactions. The indentures also provide that if any of our subsidiaries guarantee any of our indebtedness at any time in the future, then we will cause our senior notes to be equally and ratably guaranteed by that subsidiary.