Stock-based Compensation

12 Months Ended

Dec. 31, 2020

Share-based Payment Arrangement, Noncash Expense [Abstract]

Stock Compensation Plans

Pursuant to a stockholder approved plan, the Company has and is permitted to grant stock-based awards to certain employees, consultants or non-employee directors of the Company and its subsidiaries or affiliates. As of December 31, 2021, the Company has approximately 7 million shares available for future issuance pursuant to its 2013 Long-Term Incentive Plan ("LTI Plan"). Of the shares remaining available for future issuance, approximately 2 million shares may be issued pursuant to outstanding RSUs granted under the LTI Plan.

Restricted Stock Units

The Company issues RSUs to certain executives and employees. Each RSU represents a contingent right to receive one share of the Company's common stock subject to satisfaction of the applicable vesting terms. The RSUs granted to certain executives and employees include (1) annual performance awards that generally include provisions for forfeiture by the employee if certain market performance of the Company's common stock (as further described below) is not achieved, (2) new hire or promotional awards that generally contain only service-based vesting conditions and (3) other awards related to specific business initiatives or compensation objectives including retention and merger integration. Generally, such awards vest over periods of approximately three years.

The following is a summary of the RSU activity during the year ended December 31, 2021.


			RSUs
			(In millions)
Outstanding at the beginning of year			2
Granted			1
Vested			(1)
Forfeited			—
Outstanding at end of year			2

The Company granted approximately one million RSUs to the Company's executives and certain other employees for each of the years ended December 31, 2021, 2020 and 2019. The weighted-average grant-date fair value per share of the grants for the years ended December 31, 2021, 2020 and 2019 was $155.01, $160.78 and $106.55 per share, respectively. The weighted-average requisite service period for the RSUs granted during 2021 was approximately 2.3 years.

Of the approximately one million RSUs granted during the year ended December 31, 2021, (1) approximately 0.6 million RSUs were subject to time-based vesting conditions, vesting over a three-year period and (2) approximately 0.4 million RSUs were granted to the Company's executives and certain other employees and may vest on the third anniversary of the grant date based upon (a) the Company's total stockholder returns (defined as share price appreciation plus the value of dividends paid during the performance period) and (b) the Company's total stockholder return compared to that of the companies in the Standard & Poor's 500 Index. Certain RSU agreements contain provisions that result in forfeiture by the employee of any unvested shares in the event that the Company's common stock does not achieve certain performance targets. To the extent that the requisite service is rendered, compensation cost for accounting purposes is not reversed; rather, it is recognized regardless of whether or not the market performance target is achieved.

The following table summarizes the assumptions used in the Monte Carlo simulation to determine the grant-date fair value for the RSUs with market conditions granted during the years ended December 31, 2021, 2020 and 2019.


	Years Ended December 31,
	2021		2020		2019
Risk-free rate	0.2	%	1.4	%	2.5	%
Expected volatility	30	%	19	%	18	%
Expected dividend rate	3.4	%	3.5	%	4.0	%

The Company recognized aggregate stock-based compensation expense related to RSUs of $110 million, $111 million and $96 million for the years ended December 31, 2021, 2020 and 2019, respectively. The aggregate unrecognized compensation (net of estimated forfeitures) related to RSUs at December 31, 2021 is $97 million and is estimated to be recognized over a weighted-average period of less than one year.

The following table is a summary of the RSUs vested during the years ended December 31, 2021, 2020 and 2019.


Years Ended December 31,	Total Shares Vested	Fair Value on Vesting Date
	(In millions of shares)
2021	1	$	199
2020	1	220
2019	1	135

Stock-based Compensation

The following table discloses the components of stock-based compensation expense.


	Years Ended December 31,
	2021		2020		2019
Stock-based compensation expense:
Site rental costs of operations	$	14	$	16	$	19
Services and other costs of operations	8		8		7
Selling, general and administrative expenses	109		109		90
Total stock-based compensation	$	131	$	133	$	116