Debt - Details of the Liability Component (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Lease financing obligations	$ 1,000,000	$ 1,000,000
Debt issuance costs	(4,000,000)	(6,000,000)
Current portion of long-term debt	653,000,000	472,000,000
Debt issuance costs	(12,000,000)	(11,000,000)
Long-term debt	1,318,000,000	975,000,000
Lease financing obligations	198,000,000	198,000,000
Principal Balance	2,041,000,000
Long-term Debt and Capital Lease Obligations, Including Current Maturities	2,169,000,000	1,645,000,000
Convertible Debt \| 1.125% Convertible Notes
Debt Instrument [Line Items]
Current portion of long-term debt	499,000,000	477,000,000
Principal Balance	550,000,000
Convertible Debt \| 1.625% Convertible Notes
Debt Instrument [Line Items]
Current portion of long-term debt	157,000,000	0
Non-current portion of long-term debt	0	286,000,000
Principal Balance	161,000,000
Senior Notes \| 5.375% Notes
Debt Instrument [Line Items]
Non-current portion of long-term debt	700,000,000	700,000,000
Principal Balance	700,000,000
Senior Notes \| 4.875% Notes
Debt Instrument [Line Items]
Non-current portion of long-term debt	330,000,000	0
Principal Balance	330,000,000
Credit Facility
Debt Instrument [Line Items]
Non-current portion of long-term debt	300,000,000	$ 0
Principal Balance	$ 300,000,000

Long-Term Debt, Current Maturities, Net Of Unamortized Premium (Discount)

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- Definition

Long-Term Debt, Noncurrent, Net Of Unamortized Debt Discount

+ References

No definition available.

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- Definition

Amount of capital lease obligation due within one year or the normal operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (b)
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Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal, through the balance sheet date and due to be paid more than one year (or one operating cycle, if longer) after the balance sheet date.

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- Definition

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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- Definition

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 issuance costs classified as current. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Amount, after accumulated amortization, of debt issuance costs classified as noncurrent. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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- Definition

Amount of long-term debt and capital leases due within one year or the normal operating cycle, if longer.

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Amount of long-term debt and capital lease obligations including current maturities.

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Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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