STOCK-BASED EMPLOYEE COMPENSATION (Tables)

9 Months Ended

Sep. 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 nine months ended September 30, 2020: 

Restricted Stock Units	Shares	Weighted-average Grant-date Fair Value Per Share
Unvested at December 31, 2019	256,745		$	1,801
Granted	216,229		$	1,646
Vested	(123,872)		$	1,820
Forfeited	(28,043)		$	1,766
Unvested at September 30, 2020	321,059		$	1,692

Activity of Unvested Performance Share Units

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

Performance Share Units	Shares	Weighted-average Grant-date Fair Value Per Share
Unvested at December 31, 2019	216,083		$	1,835
Granted	5,540		$	2,373
Vested	(81,839)		$	1,741
Performance Shares Adjustment *	(50,209)		$	1,944
Forfeited	(4,896)		$	1,834
Unvested at September 30, 2020	84,679		$	1,893

* Probable outcome for these performance-based awards is updated based upon changes in actual and forecasted operating results or expected achievement of performance goals, as applicable, and the impact of modifications.

Estimated Vesting of Performance Share Units Granted

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

Performance Share Units, by grant year	2020	2019	2018
Shares probable to be issued	5,540	43,625	35,514
Shares not subject to the achievement of minimum performance thresholds	—	43,625	35,514
Shares that could be issued if maximum performance thresholds are met	11,080	114,086	62,547

Stock Option Valuation Assumptions

The following table summarizes the assumptions used to value option grants granted during the nine months ended September 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 nine months ended September 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	(13,093)		$	465
Forfeited	(2,555)		$	1,410
Balance, September 30, 2020	162,968		$	1,401		$	50	9.5
Exercisable at September 30, 2020	2,078		$	638		$	2	2.4