Stock Based Awards and Other Equity Instruments - Summary of Stock Option Activity (Details) - Stock Options - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Options Outstanding
Options Outstanding, Beginning balance		6,853,000	5,818,000		5,720,000
Options Outstanding, Granted		762,124	2,333,000	[1]	1,064,000
Options Outstanding, Exercised	[2]	(1,162,000)	(496,000)		(733,000)
Options Outstanding, Cancelled or expired		(412,000)	(802,000)		(233,000)
Options Outstanding, Ending balance		6,041,000	6,853,000		5,818,000
Options Outstanding, Exercisable		3,217,000
Options Outstanding, Vested and expected to vest	[3]	6,041,000
Weighted Average Exercise Price per share
Options Outstanding, Weighted Average Exercise Price, Beginning Balance		$ 52.78	$ 57.60		$ 53.71
Options Granted, Weighted Average Exercise Price		43.53	40.03	[1]	63.43
Options Exercised, Weighted Average Exercise Price	[2]	37.26	29.37		31.58
Options Cancelled or expired, Weighted Average Exercise Price		61.46	65.13		70.76
Options Outstanding, Weighted Average Exercise Price, Ending balance		54.00	$ 52.78		$ 57.60
Options Exercisable, Weighted Average Exercise Price		61.85
Options Vested and expected to vest, Weighted Average Exercise Price	[3]	$ 54.00
Weighted Average Remaining Contractual Life and Aggregate Intrinsic Value
Options Outstanding, Weighted Average Remaining Contractual Life		6 years 6 months
Options Exercisable, Weighted Average Remaining Contractual Life		4 years 8 months 12 days
Options Vested and expected to vest, Weighted Average Remaining Contractual Life	[3]	6 years 6 months
Options Outstanding, Aggregate Intrinsic Value		$ 47
Options Exercisable, Aggregate Intrinsic Value		15
Options Vested and expected to vest, Aggregate Intrinsic Value	[3]	$ 47

[1] Inclusive of 780,000 stock options awarded to our Chief Executive Officer and President, or CEO, during November 2017. The estimated grant-date fair value per option, using a Black-Scholes option pricing model was $17.33. These stock options shall vest in equal installments on each of August 1, 2021 and August 1, 2022, subject to the CEO’s continuous employment with, or performance of services for, the Company. The estimated grant-date fair value of this award will be amortized on a straight-line basis over the requisite service period through August 1, 2022.

[2] Inclusive of 814,635, 294,410, and 318,773 options as of December 31, 2018, 2017 and 2016, respectively, 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 had been convertible under stock options that were withheld under net share settlement 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 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 vested and expected to vest calculation unless necessary for a performance condition award.