Debt - Additional Information (Details) $ / shares in Units, shares in Millions				3 Months Ended	12 Months Ended
	Nov. 15, 2017 USD ($)	Feb. 01, 2017 $ / shares	Apr. 30, 2014 USD ($) $ / shares shares	Jun. 30, 2014 USD ($)	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Nov. 30, 2017 USD ($)	Jan. 31, 2017 USD ($)
Debt Instrument [Line Items]
Proceeds from 2027 notes, net of issuance costs					$ 741,039,000	$ 0	$ 0
Stock repurchase program, authorized amount				$ 1,500,000,000	8,500,000,000			$ 1,700,000,000.0	$ 500,000,000
Payments for repurchase of common stock					1,174,957,000	28,689,000	$ 755,704,000
Temporary equity					0	79,495,000
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		$ 1,386,324,000	1,348,156,000
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		0.0139061	0.011111
Convertible debt, conversion price (in dollars per share) | $ / shares					$ 90.00
Repurchase price as a percent of principal amount (percent)			100.00%
Effective interest rate (percent)					3.00%
Deferred tax liability					$ 8,200,000
Temporary equity					$ 0	$ 79,495,000
Shares of common stock covered by note hedges (shares) | shares			16.0
Additional warrant transaction (shares) | shares			16.0
Adjustment to number of shares of common stock covered by Bond Hedges and Warrant Transactions (in shares) | shares					20.0
Initial strike price of warrants (per share) | $ / shares		$ 95.25	$ 120.0
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%
GetGo, Inc [Member]
Debt Instrument [Line Items]
Convertible debt, conversion ratio		0.0139061
GetGo, Inc [Member] | Senior Notes Due 2019
Debt Instrument [Line Items]
Convertible debt, conversion price (in dollars per share) | $ / shares		$ 71.91