Debt (Convertible Debenture Details) (Details) $ / shares in Units, $ in Millions	6 Months Ended
Jun. 30, 2019 USD ($) $ / shares	Dec. 31, 2018 USD ($)
Debt Instrument [Line Items]
Net debt carrying amount	$ 1,042	$ 1,030
Convertible Debt [Member]
Debt Instrument [Line Items]
Outstanding principal amount	267
Unamortized debt discount	86
Net debt carrying amount	179
Equity component carrying amount	$ 97
Conversion rate (shares of common stock per $1,000 of principal)	13.8964
Effective conversion price (per $1,000 of principal amount) per share \| $ / shares	$ 71.9607

Carrying amount of long-term convertible debt as of the balance sheet date, net of the amount due in the next twelve months or greater than the normal operating cycle, if longer. The debt is convertible into another form of financial instrument, typically the entity's common stock.

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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 carrying amount of the equity component of convertible debt which may be settled in cash upon conversion.

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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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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, after accumulated amortization, of debt discount.

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