Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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The price per share of the conversion feature embedded in the debt instrument.

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Ratio applied to the conversion of debt instrument into equity with equity shares divided by debt principal amount.

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The amount by which the convertible debt's if-converted value exceeds its principle amount at the balance sheet date, regardless of whether the instrument is currently convertible. This element applies to public companies only.

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Remaining amortization period for discount on the liability component of convertible debt which may be settled in cash upon conversion, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of the required periodic payments including both interest and principal payments.

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Amount of the required periodic payments applied to principal.

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Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

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The cash outflow during the period from the repayment of aggregate short-term and long-term debt. Excludes payment of capital lease obligations.

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Debt - Convertible Notes (Details) $ / shares in Units, $ in Millions	1 Months Ended	12 Months Ended
	Jan. 31, 2020 USD ($)	Dec. 31, 2019 USD ($) $ / shares	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
(Gain) loss on debt extinguishment		$ (15)	$ 22	$ 14
Net carrying amount of debt		$ 1,262
1.125% Convertible Notes
Debt Instrument [Line Items]
Percentage of contractual interest rate on notes		1.125%
4.875% Notes
Debt Instrument [Line Items]
Percentage of contractual interest rate on notes		4.875%
5.375% Notes
Debt Instrument [Line Items]
Percentage of contractual interest rate on notes		5.375%
Convertible Debt \| 1.125% Convertible Notes
Debt Instrument [Line Items]
Percentage of contractual interest rate on notes		1.125%
Repayments of debt		$ 794	911
Repayments of principal		240	298
Repayment of aggregate carrying amount		232	278
(Gain) loss on debt extinguishment		15	(12)
Net carrying amount of debt		$ 12
Debt instrument, conversion ratio		0.0245277
Debt instrument conversion price per share (in dollars per share) \| $ / shares		$ 40.77
Senior note effective interest rate		6.00%
Senior notes amortization period		1 month
If-converted value in excess of principal on convertible debt		$ 26	$ 581
Convertible Debt \| 4.875% Notes
Debt Instrument [Line Items]
Percentage of contractual interest rate on notes		4.875%
Convertible Debt \| Convertible Senior Notes
Debt Instrument [Line Items]
Debt instrument, conversion ratio		0.0172157
Convertible Debt \| Subsequent Event \| 1.125% Convertible Notes
Debt Instrument [Line Items]
Percentage of contractual interest rate on notes	1.125%
Repayments of principal	$ 39