Stock Based Awards and Other Equity Instruments - Summary of Stock Option Activity (Details) - Stock Options - USD ($) $ / shares in Units, shares in Thousands, $ in Millions		6 Months Ended
		Jun. 30, 2021
Options Outstanding
Options Outstanding, Beginning balance		5,615
Options Outstanding, Granted		716
Options Outstanding, Exercised	[1]	(672)
Options Outstanding, Cancelled or expired		(152)
Options Outstanding, Ending balance		5,507
Options Outstanding, Exercisable		3,341
Options Outstanding, Vested and expected to vest	[2]	5,507
Weighted Average Exercise Price per share
Options Outstanding, Weighted Average Exercise Price, Beginning Balance		$ 46.31
Options Granted, Weighted Average Exercise Price		46.00
Options Exercised, Weighted Average Exercise Price	[1]	34.40
Options Cancelled or expired, Weighted Average Exercise Price		42.57
Options Outstanding, Weighted Average Exercise Price, Ending balance		47.83
Options Exercisable, Weighted Average Exercise Price		54.65
Options Vested and expected to vest, Weighted Average Exercise Price	[2]	$ 47.83
Weighted Average Remaining Contractual Life and Aggregate Intrinsic Value
Options Outstanding, Weighted Average Remaining Contractual Life		5 years 4 months 24 days
Options Exercisable, Weighted Average Remaining Contractual Life		3 years 7 months 6 days
Options Vested and expected to vest, Weighted Average Remaining Contractual Life	[2]	5 years 4 months 24 days
Options Outstanding, Aggregate Intrinsic Value		$ 19
Options Exercisable, Aggregate Intrinsic Value		6
Options Vested and expected to vest, Aggregate Intrinsic Value	[2]	$ 19

[1] Inclusive of approximately 371,000 stock options which were not converted into shares due to net share settlement in order to cover the aggregate exercise price and the required amount of employee withholding taxes. Potential shares which were withheld in connection with exercised stock options due to net share settlement to satisfy required employee tax withholding requirements and payment of the aggregate exercise price remain in the authorized but unissued pool under the 2018 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.

[2] 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 vested and expected to vest calculation unless necessary for a performance condition award.