Stock Based Awards and Other Equity Instruments - Summary of RSU Activity, Including Service Based Awards and Performance-Based Awards (Details) - Restricted Stock Units $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($) $ / shares shares
RSUs outstanding
Unvested outstanding, Beginning balance | shares	6,015
Unvested RSUs, Transfer | shares	(213)	[1]
Unvested RSUs, Granted | shares	2,590
Unvested RSUs, Vested and released | shares	(1,007)	[2]
Unvested RSUs, Cancelled | shares	(160)
Unvested outstanding, Ending balance | shares	7,225
RSUs outstanding, Expected to vest | shares	7,225	[3]
Weighted Average Grant-Date Fair Value Per Share
Unvested outstanding, Weighted Average Grant-Date Fair Value Per Share, Beginning balance | $ / shares	$ 48.14
Weighted Average Grant-Date Fair Value Per Share, Transfer | $ / shares	30.04	[1]
Weighted Average Grant-Date Fair Value Per Share, Granted | $ / shares	41.44
Weighted Average Grant-Date Fair Value Per Share, Vested and released | $ / shares	56.11	[2]
Weighted Average Grant-Date Fair Value Per Share, Cancelled | $ / shares	47.26
Unvested outstanding, Weighted Average Grant-Date Fair Value Per Share, Ending balance | $ / shares	45.18
Weighted Average Grant-Date Fair Value Per Share, Expected to vest | $ / shares	$ 45.18	[3]
Aggregate Intrinsic Value
Unvested RSUs outstanding, Aggregate Intrinsic Value | $	$ 295
RSUs Vested and expected to vest, Aggregate Intrinsic Value | $	$ 295

[1] RSUs outstanding as of December 31, 2017 include 213,000 MSUs awarded to the Company’s CEO in November 2017. This award has been transferred to the MSU activity table below.

[2] Inclusive of 269,878 RSUs withheld due to net share settlement to satisfy required employee tax withholding requirements. Potential shares which had been convertible under RSUs that were withheld under net share settlement remain in the authorized but unissued pool under the 2011 Incentive Plan and can be reissued by the Company. Total payments for the employees’ tax obligations to the taxing authorities due to net share settlements are reflected as a financing activity within the unaudited condensed consolidated statements of cash flows.

[3] The Company accounts for forfeitures as they occur, rather than estimate expected forfeitures as allowed under GAAP and therefore do not include a forfeiture rate in our expected to vest calculation unless necessary for a performance condition award.