Debt and Capital Leases - Convertible Senior Notes (Details)	6 Months Ended
Jun. 30, 2018 USD ($) $ / shares
Debt Instrument [Line Items]
Transaction costs in connection with issuance	$ 12,000,000
Convertible Debt \| Convertible Senior Notes due 2048
Debt Instrument [Line Items]
Aggregate principal amount	$ 575,000,000
Interest rate, stated percentage	2.75%
Conversion price (in usd per share) \| $ / shares	$ 47.74
Conversion ratio	20.9479
Carrying amount of liability component	$ 472,000,000
Carrying amount of equity component	$ 103,000,000
Debt discount amortization period (years)	7 years
Deferred financing costs, amortization period	7 years
Convertible Debt \| Convertible Senior Notes due 2048 \| Additional Paid-in Capital
Debt Instrument [Line Items]
Transaction costs in connection with issuance	$ 2,000,000
Convertible Debt \| Convertible Senior Notes due 2048 \| Deferred Financing Costs
Debt Instrument [Line Items]
Transaction costs in connection with issuance	$ 9,500,000

Amortization Period, Debt Issuance Costs

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- Definition

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

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
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- Definition

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

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- Definition

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

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- Definition

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.

+ References

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-Publisher FASB
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- Definition

Face (par) amount of debt instrument at time of issuance.

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- Definition

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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- Definition

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

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The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

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