Debt - Additional Information (Details) $ / shares in Units, shares in Thousands			1 Months Ended	3 Months Ended		12 Months Ended
	Nov. 15, 2017 USD ($)	Apr. 30, 2014 USD ($) shares	Sep. 30, 2018 USD ($) day $ / shares	Dec. 31, 2018 USD ($) $ / shares shares	Jun. 30, 2014 USD ($)	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Oct. 31, 2018 USD ($)	Nov. 30, 2017 USD ($)	Dec. 31, 2014
Debt Instrument [Line Items]
Proceeds from 2027 notes, net of issuance costs						$ 0	$ 741,039,000	$ 0
Stock repurchase program, authorized amount					$ 1,500,000,000				$ 750,000,000	$ 1,700,000,000.0
Payments for repurchase of common stock						1,261,153,000	1,174,957,000	$ 28,689,000
Convertible notes, short-term				$ 1,155,445,000		1,155,445,000	0
Temporary equity				8,110,000		8,110,000	0
Convertible Debt, Conversion Notices Received, Amount			$ 273,000,000
Senior Notes Due 2019
Debt Instrument [Line Items]
Principal amount of notes				1,000		1,000
Stated interest rate (percent)											0.50%
Convertible debt		$ 1,440,000,000		$ 1,155,445,000		$ 1,155,445,000	1,386,324,000
Proceeds from convertible debt offering		1,420,000,000
Net proceeds used to pay the cost of Bind Hedges		$ 82,600,000
Convertible debt, conversion ratio						0.0139510
Convertible debt, conversion price (in dollars per share) | $ / shares				$ 71.68		$ 71.68
Repurchase price as a percent of principal amount (percent)		100.00%
Effective interest rate (percent)						3.00%
Convertible Debt, Noncurrent				$ 1,400,000,000		$ 1,400,000,000
Deferred tax liability				8,200,000		8,200,000
Temporary equity				$ 8,110,000		$ 8,110,000	$ 0
Shares of common stock covered by note hedges (shares) | shares		16,000
Additional warrant transaction (shares) | shares		16,000
Adjustment to number of shares of common stock covered by Bond Hedges and Warrant Transactions (in shares) | shares						20,000
Initial strike price of warrants (per share) | $ / shares				$ 94.94		$ 94.94
Debt Instrument, Convertible, Threshold Trading Days | day			20
Debt Instrument, Convertible, Threshold Consecutive Trading Days | day			30
Debt Instrument, Convertible, Threshold Percentage of Stock Price Trigger			130.00%
Privately Negotiated Transaction
Debt Instrument [Line Items]
Payments for repurchase of common stock					101,000,000
Purchase From Accelerated Share Repurchase
Debt Instrument [Line Items]
Shares repurchased under the ASR					$ 1,400,000,000
Unsecured Debt [Member] | Unsecured Senior Notes due December 2027 [Member]
Debt Instrument [Line Items]
Principal amount of notes	$ 750,000,000
Stated interest rate (percent)	4.50%
Proceeds from 2027 notes, net of issuance costs	$ 741,000,000
Prior to September 1, 2017 [Member] | Unsecured Debt [Member] | Unsecured Senior Notes due December 2027 [Member]
Debt Instrument [Line Items]
Redemption price, as percentage of aggregate principal amount (percent)	100.00%
Upon Change of Control Prior to Maturity [Member] | Unsecured Debt [Member] | Unsecured Senior Notes due December 2027 [Member]
Debt Instrument [Line Items]
Redemption price, as percentage of aggregate principal amount (percent)	101.00%
Minimum | Senior Notes Due 2019
Debt Instrument [Line Items]
Debt Instrument, Convertible, Threshold Trigger Stock Price | $ / shares			$ 93.48
Common Stock
Debt Instrument [Line Items]
Settlement of convertible notes and hedges (shares) | shares				1,300		1,291