Debt

Our long-term debt consisted of the following as of March 31, 2018 and December 31, 2017:



	March 31, 2018						December 31, 2017
	Principal Amount			Carrying Amount			Principal Amount			Carrying Amount
	($ in millions)
7.25% senior notes due 2018	$	44		$	44		$	44		$	44
Floating rate senior notes due 2019	380			380			380			380
6.625% senior notes due 2020	437			437			437			437
6.875% senior notes due 2020	227			227			227			227
6.125% senior notes due 2021	548			548			548			548
5.375% senior notes due 2021	267			267			267			267
4.875% senior notes due 2022	451			451			451			451
8.00% senior secured second lien notes due 2022	1,416			1,870			1,416			1,895
5.75% senior notes due 2023	338			338			338			338
8.00% senior notes due 2025	1,300			1,290			1,300			1,290
5.5% convertible senior notes due 2026^(a)(b)	1,250			844			1,250			837
8.00% senior notes due 2027	1,300			1,298			1,300			1,298
2.25% contingent convertible senior notes due 2038^(a)	9			8			9			8
Term loan due 2021	1,233			1,233			1,233			1,233
Revolving credit facility	200			200			781			781
Debt issuance costs	—			(60		)	—			(63		)
Interest rate derivatives	—			2			—			2
Total debt, net	9,400			9,377			9,981			9,973
Less current maturities of long-term debt, net^(c)	(53		)	(52		)	(53		)	(52		)
Total long-term debt, net	$	9,347		$	9,325		$	9,928		$	9,921

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(a)

We are required to account for the liability and equity components of our convertible debt instruments separately and to reflect interest expense through the first demand repurchase date, as applicable, at the interest rate of similar nonconvertible debt at the time of issuance. The applicable rates for our 2.25% Contingent Convertible Senior Notes due 2038 and our 5.5% Convertible Senior Notes due 2026 are 8.0% and 11.5%, respectively.


(b)	Prior to maturity under certain circumstances and at the holder’s option, the notes are convertible. During the first quarter of 2018, the price of our common stock was below the threshold level for conversion and, as a result, the holders do not have the option to convert their notes in the second quarter of 2018.


(c)	As of March 31, 2018, current maturities of long-term debt, net includes our 7.25% Senior Notes due December 2018 and our 2.25% Contingent Convertible Notes due December 2038.

Debt Retirements

In the Prior Quarter, we retired $908 million principal amount of our outstanding senior notes and contingent convertible notes through purchases in the open market, tender offers or repayment upon maturity for $982 million. For the open market repurchases and tender offers, we recorded an aggregate net loss of approximately $7 million.

Revolving Credit Facility

We have a senior secured revolving credit facility currently subject to a $3.8 billion borrowing base that matures in December 2019. As of March 31, 2018, we had outstanding borrowings of $200 million under the revolving credit facility and had used $157 million of the revolving credit facility for various letters of credit. Borrowings under the revolving credit facility bear interest at a variable rate. The terms of the revolving credit facility include covenants limiting, among other things, our ability to incur additional indebtedness, make investments or loans, create liens, consummate mergers and similar fundamental changes, make restricted payments, make investments in unrestricted subsidiaries and enter into transactions with affiliates. Our next borrowing base redetermination is scheduled for the second quarter of 2018.

Our revolving credit facility is subject to various financial and other covenants. As of March 31, 2018, we were in compliance with all applicable financial covenants under the credit agreement and we were able to borrow up to the full availability under the revolving credit facility.

Fair Value of Debt

We estimate the fair value of our senior notes based on the market value of our publicly traded debt as determined based on the yield of our senior notes (Level 1). The fair value of all other debt is based on a market approach using estimates provided by an independent investment financial data services firm (Level 2). Fair value is compared to the carrying value, excluding the impact of interest rate derivatives, in the table below:



	March 31, 2018				December 31, 2017
	Carrying Amount		Estimated Fair Value		Carrying Amount		Estimated Fair Value
			($ in millions)
Short-term debt (Level 1)	$	52	$	53	$	52	$	53
Long-term debt (Level 1)	$	2,635	$	2,603	$	2,633	$	2,629
Long-term debt (Level 2)	$	6,690	$	6,582	$	7,286	$	7,301