EMPLOYEE BENEFIT PLANS - Restricted Stock Units (Details) $ / shares in Units, $ in Millions	1 Months Ended	9 Months Ended
May 31, 2018 director shares	Sep. 30, 2018 USD ($) $ / shares shares
Weighted Average Grant Date Fair Value Per Unit
Number of newly appointed directors \| director	2
Restricted Stock Units
Restricted Stock Units
Unvested at the beginning of the period (in shares)		2,253,988
Granted (in shares)	12,154	734,091
Vested (in shares)		(872,062)
Forfeited (in shares)		(128,074)
Unvested at the end of the period (in shares)		1,987,943
Weighted Average Grant Date Fair Value Per Unit
Unvested at the beginning of the period (in dollars per share) \| $ / shares		$ 35.20
Granted (in dollars per share) \| $ / shares		24.70
Vested (in dollars per share) \| $ / shares		34.03
Forfeited (in dollars per share) \| $ / shares		36.24
Unvested at the end of the period (in dollars per share) \| $ / shares		$ 31.77
Vesting period		3 years
Percentage of restricted stock units, which will vest three years from the grant date		33.33%
Unrecognized compensation costs \| $		$ 22
Period for recognition of unrecognized compensation costs		1 year 7 months 6 days
Restricted Stock Units \| Non-Employee Director
Restricted Stock Units
Granted (in shares)	54,198
Restricted Stock Units \| Director
Restricted Stock Units
Granted (in shares)	3,670
Restricted Stock Units \| Vesting and settled ratably over a three-year period from the grant date
Restricted Stock Units
Granted (in shares)		288,325
Weighted Average Grant Date Fair Value Per Unit
Vesting period		3 years
Restricted Stock Units \| Vesting and settled ratably over a two-year period from the grant date
Restricted Stock Units
Granted (in shares)		339,806
Weighted Average Grant Date Fair Value Per Unit
Vesting period		2 years
Restricted Stock Units \| Vesting and settled on the third anniversary of the grant date
Restricted Stock Units
Granted (in shares)		29,870
Restricted Stock Units \| Performance-based vesting
Restricted Stock Units
Granted (in shares)		6,068
Restricted Stock Units \| Performance-based vesting \| Minimum
Weighted Average Grant Date Fair Value Per Unit
Percentage of restricted stock units, which will vest three years from the grant date		0.00%
Restricted Stock Units \| Performance-based vesting \| Maximum
Weighted Average Grant Date Fair Value Per Unit
Percentage of restricted stock units, which will vest three years from the grant date		200.00%

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Unrecognized cost of unvested share-based compensation awards.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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 number of grants made 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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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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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting 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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Percentage of vesting of share-based compensation awards.

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