STOCKHOLDER'S EQUITY - Restricted Stock Activity (Details) - Restricted Stock Awards (RSAs) and Restricted Stock Units (RSUs)	12 Months Ended
Dec. 31, 2019 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting term	4 years
Number of shares
Beginning balance (in shares) \| shares	17,934,728
Granted (in shares) \| shares	7,028,055
Vested (in shares) \| shares	(8,023,399)
Forfeited (in shares) \| shares	(3,021,923)
Ending balance (in shares) \| shares	13,917,461
Weighted Average Grant Date Fair Value
Beginning balance (in USD per share) \| $ / shares	$ 31.34
Granted (in USD per share) \| $ / shares	70.61
Vested (in USD per share) \| $ / shares	30.19
Forfeited (in USD per share) \| $ / shares	40.25
Ending balance (in USD per share) \| $ / shares	$ 49.90

Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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