Stockholders' Equity

1.125% Warrants

In connection with the Call Spread Overlay transaction described in Note 8, “Derivatives,” in 2013, we issued 13.5 million warrants with a strike price of $53.8475 per share. Under certain circumstances, beginning in April 2020, if the price of our common stock exceeds the strike price of the 1.125% Warrants, we will be obligated to issue shares of our common stock subject to a share delivery cap. The 1.125% Warrants could separately have a dilutive effect to the extent that the market value per share of our common stock exceeds the applicable strike price of the 1.125% Warrants. Refer to Note 3, “Net Income per Share,” for dilution information for the periods presented. We will not receive any additional proceeds if the 1.125% Warrants are exercised. Following the transactions described below, 5.1 million of the 1.125% Warrants remain outstanding.

As described in Note 8, “Derivatives,” in the first quarter of 2019, we entered into privately negotiated termination agreements with each of the Counterparties to partially terminate the Call Spread Overlay, in notional amounts corresponding to the aggregate principal amount of the 1.125% Convertible Notes purchased. In the first quarter of 2019, we paid $103 million to the Counterparties for the termination of 1.1 million of the 1.125% Warrants outstanding, which resulted in a reduction of additional paid-in-capital for the same amount.

Subsequent Event

In April 2019, we entered into privately negotiated termination agreements with each of the Counterparties to partially terminate the Call Spread Overlay, in notional amounts corresponding to the aggregate principal amount of the 1.125% Convertible Notes purchased. Pursuant to these transactions, we paid $298 million to the Counterparties for the termination of 3.1 million of the 1.125% Warrants outstanding, which resulted in a reduction of additional paid-in-capital for the same amount.

Share-Based Compensation

In connection with our employee stock plans, approximately 84,000 shares of common stock vested or were purchased, net of shares used to settle employees’ income tax obligations, during the three months ended March 31, 2019.

Share-based compensation is generally recorded to “General and administrative expenses” in the accompanying consolidated statements of income. Total share-based compensation expense for the three months ended March 31, 2019 and 2018, amounted to $9 million and $6 million, respectively.

As of March 31, 2019, there was $71 million of total unrecognized compensation expense related to unvested restricted stock awards (“RSAs”), and performance stock units (“PSUs”), which we expect to recognize over a remaining weighted-average period of 2.9 years and 2.3 years, respectively. This unrecognized compensation cost assumes an estimated forfeiture rate of 14.1% for non-executive employees as of March 31, 2019.

Also as of March 31, 2019, there was $8 million of total unrecognized compensation expense related to unvested stock options, which we expect to recognize over a weighted-average period of 1.5 years. No stock options were granted or exercised in the three months ended March 31, 2019.

Activity for RSAs, performance stock awards (“PSAs”) and PSUs, for the three months ended March 31, 2019, is summarized below:



	RSAs		PSAs		PSUs		Total		Weighted Average Grant Date Fair Value
Unvested balance, December 31, 2018	399,795		3,132		201,383		604,310		$	71.50
Granted	215,178		—		138,994		354,172		137.37
Vested	(119,994	)	(3,132	)	(10,528	)	(133,654	)	68.24
Forfeited	(14,220	)	—		(4,140	)	(18,360	)	74.03
Unvested balance, March 31, 2019	480,759		—		325,709		806,468		100.91

The aggregate fair values of RSAs, PSAs and PSUs granted and vested are presented in the following table:



	Three Months Ended March 31,
	2019		2018
	(In millions)
Granted:
RSAs	$	30	$	23
PSUs	18		14
	$	48	$	37
Vested:
RSAs	$	16	$	12
PSUs	2		—
PSAs	—		3
	$	18	$	15