Our long-term debt consisted of the following as of March 31, 2016 and December 31, 2015:



	March 31, 2016						December 31, 2015
	Principal Amount			Carrying Amount			Principal Amount			Carrying Amount
	($ in millions)
3.25% senior notes due 2016	$	—		$	—		$	381		381
6.25% euro-denominated senior notes due 2017^(a)	344			344			329			329
6.5% senior notes due 2017	379			379			453			453
7.25% senior notes due 2018	538			538			538			538
Floating rate senior notes due 2019	1,104			1,104			1,104			1,104
6.625% senior notes due 2020	822			822			822			822
6.875% senior notes due 2020	304			304			304			304
6.125% senior notes due 2021	589			589			589			589
5.375% senior notes due 2021	286			286			286			286
4.875% senior notes due 2022	639			639			639			639
8.00% senior secured second lien notes due 2022	2,425			3,542			2,425			3,584
5.75% senior notes due 2023	384			384			384			384
2.75% contingent convertible senior notes due 2035^(b)	2			2			2			2
2.5% contingent convertible senior notes due 2037^(b)(c)	902			846			1,110			1,027
2.25% contingent convertible senior notes due 2038^(b)(c)	340			293			340			290
Revolving credit facility	367			367			—			—
Debt issuance costs	—			(38		)	—			(43		)
Discount on senior notes	—			(3		)	—			(4		)
Interest rate derivatives^(d)	—			7			—			7
Total debt, net	9,425			10,405			9,706			10,692
Less current maturities of long-term debt, net^(e)	(344		)	(343		)	(381		)	(381		)
Total long-term debt, net	$	9,081		$	10,062		$	9,325		$	10,311

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(a)	The principal and carrying amounts shown are based on the exchange rate of $1.1380 to €1.00 and $1.0862 to €1.00 as of March 31, 2016 and December 31, 2015, respectively. See Foreign Currency Derivatives in Note 8 for information on our related foreign currency derivatives.


(b)	The repurchase, conversion, contingent interest and redemption provisions of our contingent convertible senior notes are as follows:

Holders’ Demand Repurchase Rights. The holders of our contingent convertible senior notes may require us to repurchase, in cash, all or a portion of their notes at 100% of the principal amount of the notes on any of four dates that are five, ten, fifteen and twenty years before the maturity date.

Optional Conversion by Holders. At the holder’s option, prior to maturity under certain circumstances, the notes are convertible into cash and, if applicable, shares of our common stock using a net share settlement process. One triggering circumstance is when the price of our common stock exceeds a threshold amount during a specified period in a fiscal quarter. Convertibility based on common stock price is measured quarterly. During the specified period in the Current Quarter, the price of our common stock was below the threshold level for each series of the contingent convertible senior notes and, as a result, the holders do not have the option to convert their notes into cash and common stock in the second quarter of 2016 under this provision.

The notes are also convertible, at the holder’s option, during specified five-day periods if the trading price of the notes is below certain levels determined by reference to the trading price of our common stock. The notes were not convertible under this provision during the Current Quarter and the Prior Quarter. In general, upon conversion of a contingent convertible senior note, the holder will receive cash equal to the principal amount of the note and common stock for the note’s conversion value in excess of the principal amount.

Contingent Interest. We will pay contingent interest on the convertible senior notes after they have been outstanding at least ten years during certain periods if the average trading price of the notes exceeds the threshold defined in the indenture.

The holders’ demand repurchase dates, the common stock price conversion threshold amounts (as adjusted to give effect to cash dividends on our common stock) and the ending date of the first six-month period in which contingent interest may be payable for the contingent convertible senior notes are as follows:



Contingent Convertible Senior Notes	Holders' Demand Repurchase Dates	Common Stock Price Conversion Thresholds		Contingent Interest First Payable (if applicable)
2.75% due 2035	November 15, 2020, 2025, 2030	$	45.02	May 14, 2016
2.5% due 2037	May 15, 2017, 2022, 2027, 2032	$	59.44	November 14, 2017
2.25% due 2038	December 15, 2018, 2023, 2028, 2033	$	100.20	June 14, 2019

Optional Redemption by the Company. We may redeem the contingent convertible senior notes once they have been outstanding for ten years at a redemption price of 100% of the principal amount of the notes, payable in cash. We may redeem our 2.75% Contingent Convertible Senior Notes due 2035 at any time.


(c)	Discount as of March 31, 2016 and December 31, 2015 included $103 million and $133 million, respectively, associated with the equity component of our contingent convertible senior notes. This discount is amortized based on an effective yield method.


(d)	See Interest Rate Derivatives in Note 8 for further discussion related to these instruments.


(e)	As of March 31, 2016, current maturities of long-term debt, net includes our 6.25% Euro-denominated Senior Notes due 2017