The value of the financial instrument(s) that the original debt is being converted into in a noncash (or part noncash) transaction. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

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Derivatives (Details) - USD ($) $ in Millions	3 Months Ended
Derivatives (Details) - USD ($) $ in Millions	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Derivative [Line Items]
Cash received for partial termination of 1.125% Call Option	$ 115	$ 0
Cash paid for partial termination of 1.125% Warrants	103	$ 0
Debt conversion, net cash receipts	$ 12
1.125% Convertible Notes
Derivative [Line Items]
Percentage of contractual interest rate on Notes	1.125%
1.125% Call Option
Derivative [Line Items]
Percentage of contractual interest rate on Call Option	1.125%
1.125% Conversion Option derivative liability
Derivative [Line Items]
Percentage of contractual interest rate on Call Option	1.125%
Cash received for partial termination of 1.125% Call Option	$ 115
Current assets: Derivative asset \| 1.125% Call Option
Derivative [Line Items]
Derivative assets	516		$ 476
Current liabilities: Derivative liability \| 1.125% Conversion Option derivative liability
Derivative [Line Items]
Derivative liabilities	516		$ 476
1.125% Warrants
Derivative [Line Items]
Cash paid for partial termination of 1.125% Warrants	$ 103