EMPLOYEE BENEFIT PLANS - Restricted Stock Units (Details) - Restricted Stock Units $ / shares in Units, $ in Millions	1 Months Ended		6 Months Ended
	May 31, 2020 shares	May 31, 2019 shares	Jun. 30, 2020 USD ($) quarter $ / shares shares	Jun. 30, 2019 quarter shares
Restricted Stock Units
Unvested at the beginning of the period (in shares)			1,463,499
Granted (in shares)			1,574,325	1,235,876
Vested (in shares)			(598,037)
Forfeited (in shares)			(40,721)
Unvested at the end of the period (in shares)			2,399,066
Weighted Average Grant Date Fair Value Per Unit
Unvested at the beginning of the period (in dollars per share) | $ / shares			$ 25.08
Granted (in dollars per share) | $ / shares			28.24
Vested (in dollars per share) | $ / shares			25.20
Forfeited (in dollars per share) | $ / shares			26.72
Unvested at the end of the period (in dollars per share) | $ / shares			$ 27.10
Vesting period			3 years
Award vesting percentage			33.33%
Unrecognized compensation costs | $			$ 43
Period for recognition of unrecognized compensation costs			2 years 1 month 6 days
2013 Grant
Restricted Stock Units
Granted (in shares)				7,427
Non-Employee Directors
Restricted Stock Units
Granted (in shares)	103,434	100,444
Time based vesting, three year period from grant date
Restricted Stock Units
Granted (in shares)			517,398	243,506
Weighted Average Grant Date Fair Value Per Unit
Vesting period			3 years	3 years
Time based vesting, four year period from grant date
Restricted Stock Units
Granted (in shares)			104,167
Weighted Average Grant Date Fair Value Per Unit
Vesting period			4 years
Eleven quarter vesting period
Restricted Stock Units
Granted (in shares)			359,713
Weighted Average Grant Date Fair Value Per Unit
Vesting period, quarterly periods | quarter			11
Performance based vesting on the third anniversary
Restricted Stock Units
Granted (in shares)			409,485
Performance based vesting | Minimum
Weighted Average Grant Date Fair Value Per Unit
Award vesting percentage			0.00%
Performance based vesting | Maximum
Weighted Average Grant Date Fair Value Per Unit
Award vesting percentage			200.00%
Performance based vesting over a four year period | Officer
Restricted Stock Units
Granted (in shares)			80,128
Weighted Average Grant Date Fair Value Per Unit
Award vesting performance period			4 years
Nine quarter vesting period
Restricted Stock Units
Granted (in shares)				566,172
Weighted Average Grant Date Fair Value Per Unit
Vesting period, quarterly periods | quarter				9
Third anniversary vesting date
Weighted Average Grant Date Fair Value Per Unit
Number of restricted stock units vested on third anniversary of grant date (in shares)				318,327