STOCK-BASED EMPLOYEE COMPENSATION (Tables)

6 Months Ended

Jun. 30, 2020

Share-based Payment Arrangement [Abstract]

Activity of unvested restricted stock units

The following table summarizes the activity of restricted stock units for employees and non-employee directors during the six months ended June 30, 2020: 

Restricted Stock Units	Shares	Weighted-average Grant-date Fair Value Per Share
Unvested at December 31, 2019	256,745		$	1,801
Granted	212,913		$	1,644
Vested	(117,709)		$	1,811
Forfeited	(15,636)		$	1,784
Unvested at June 30, 2020	336,313		$	1,698

Activity of unvested performance share units

The following table summarizes the activity of performance share units for employees during the six months ended June 30, 2020:

Performance Share Units	Shares	Weighted-average Grant-date Fair Value Per Share
Unvested at December 31, 2019	216,083		$	1,835
Vested	(81,396)		$	1,740
Performance Shares Adjustment *	(50,182)		$	1,944
Forfeited	(4,547)		$	1,840
Unvested at June 30, 2020	79,958		$	1,859

Estimated vesting of performance share units granted [Table Text Block]

The following table summarizes the estimated vesting, as of June 30, 2020, of performance share units granted in 2019 and 2018, net of forfeiture and vesting since the respective grant dates:

Performance Share Units, by grant year	2019	2018
Shares probable to be issued	44,237	35,721
Shares not subject to the achievement of minimum performance thresholds	44,237	35,721
Shares that could be issued if maximum performance thresholds are met	115,310	62,606

Stock option valuation assumptions

The following table summarizes the assumptions used to value option grants granted in the six months ended June 30, 2020 using the Black-Scholes options pricing model:

Black-Scholes assumptions
Risk-free interest rate	0.56	%
Expected term in years	6.4
Expected stock price volatility	33.8	%
Expected dividend yield	0	%

Share-based payment arrangement option activity

The following table summarizes the activity for stock options during the six months ended June 30, 2020: 

Employee Stock Options	Number of Shares	Weighted-average Exercise Price			Aggregate Intrinsic Value (in millions)			Weighted-average Remaining Contractual Term (in years)
Balance, December 31, 2019	15,122		$	484		$	24	2.6
Granted	163,494		$	1,411
Exercised	(12,884)		$	464
Forfeited	(690)		$	1,411
Balance, June 30, 2020	165,042		$	1,400		$	32	9.8
Exercisable at June 30, 2020	2,238		$	616		$	2	2.5