We issue restricted stock awards to key employees under our Incentive Compensation Plan (Plan). We issue time-based awards and performance-based awards under this Plan, both of which are based on a three-year vesting period. The grant date fair value of the time-based awards is equal to the price of our common stock on the grant date. The fair value of the performance-based awards is based on a Monte-Carlo simulation valuation of our common stock as of the grant date. The assumptions used for this valuation include stock price volatility, risk-free interest rate and dividend yield. We issued 353,656 and 283,037 performance-based restricted stock units in 2019 and 2018, respectively. As of December 31, 2019, we had available up to 1,620,243 shares of common stock to issue under this Plan.

The following table details our issuance of restricted stock units and the aggregate weighted average grant date fair values under these plans for the years indicated:

The unvested restricted stock unit awards are eligible to receive cash dividends or dividend equivalents which are ultimately used to purchase additional shares of stock and are subject to forfeiture if the requisite service period is not completed or the specified performance criteria are not met. These awards are subject to certain accelerated vesting provisions upon retirement, death, disability or in the event of a change of control as defined in the award agreements.



	2019				2018				2017
	Units		Weighted Average Grant Price per Share		Units		Weighted Average Grant Price per Share		Units		Weighted Average Grant Price per Share
Unvested units outstanding at beginning of year	2,556,174		$	13.51	1,975,862		$	13.64	1,836,363		$	12.97
Granted	1,182,197		10.94		962,799		13.21		713,998		14.67
Net adjustment due to performance	—		—		—		—		(64,861	)	13.85
Vested	(655,208	)	13.15		(258,031	)	13.19		(542,580	)	12.71
Forfeited/expired	(332,814	)	12.72		(214,743	)	13.39		(31,018	)	14.03
Dividend reinvestment	108,008		11.84		90,287		12.61		63,960		13.80
Unvested units outstanding at end of year	2,858,357		12.56		2,556,174		13.51		1,975,862		13.64



Year Ended December 31	2019		2018		2017
(in millions)
Stock-based compensation expense	$	12	$	10	$	8
Tax benefit related to stock-based compensation expense	2		2		3
Fair value of units vested	7		3		8

As of December 31, 2019, there was $14.3 million of unrecognized compensation cost related to unvested restricted stock units including $0.5 million that is subject to accelerated vesting under the Plan’s immediate vesting upon retirement. The components of the restricted stock units as of December 31, 2019 are as follows:



(dollars in millions)	Service- Based Units		Performance- Based Units		Total
Unvested restricted stock units	1,922,120		936,237		2,858,357
Unrecognized compensation expense	$	10	$	4	$	14
Intrinsic value	$	24	$	12	$	36
Weighted average remaining life (in years)	1.83		1.81		1.82

All outstanding stock options were assumed from acquisitions and are fully vested. Upon consummation of our acquisitions, all outstanding stock options issued by the acquired companies were converted into equivalent FNB stock options. We issue shares of treasury stock or authorized but unissued shares to satisfy stock options exercised.



	2019		Weighted Average Exercise Price per Share		2018		Weighted Average Exercise Price per Share		2017		Weighted Average Exercise Price per Share
Options outstanding at beginning of year	458,354		$	7.99	722,650		$	7.96	892,532		$	8.95
Assumed from acquisitions	—		—		—		—		207,645		8.92
Exercised	(183,566	)	7.86		(253,899	)	7.77		(255,503	)	10.21
Forfeited/expired	(28,704	)	7.65		(10,397	)	11.98		(122,024	)	12.12
Options outstanding and exercisable at end of year	246,084		8.14		458,354		7.99		722,650		7.96



Range of Exercise Prices	Options Outstanding and Exercisable	Weighted Average Remaining Contractual Years	Weighted Average Exercise Price
$3.45 - $5.18	54,148	1.26	$	4.82
$5.19 - $7.78	40,022	3.11	6.90
$7.79 - $11.37	151,914	4.71	9.64
	246,084

The intrinsic value of outstanding and exercisable stock options at December 31, 2019 was $1.1 million. The aggregate intrinsic value represents the amount by which the fair value of underlying stock exceeds the option exercise price.

As of December 31, 2019, there were no longer any outstanding warrants. The following paragraphs summarize the warrants that were previously issued that have been exercised or expired in 2018 and 2019.

In conjunction with our participation in the UST’s CPP, we issued to the UST a warrant to purchase up to 1,302,083 shares of our common stock. Pursuant to Section 13(H) of the Warrant to Purchase Common Stock, the number of shares of common stock issuable upon exercise of the warrant was reduced in half to 651,042 shares on June 16, 2009, the date we completed a public offering. The warrant, which expired in January 2019 without being exercised, was sold at auction by the UST and had an exercise price of $11.52 per share.

In conjunction with the ANNB acquisition on April 6, 2013, the warrant issued by ANNB to the UST under the CPP has been converted into a warrant to purchase up to 342,564 shares of our common stock at an exercise price of $3.57 per share. Subsequent adjustments related to actual dividends paid by us have increased the share amount of these warrants to 405,489, with a resulting lower exercise price of $3.02 per share as of March 31, 2018, prior to being exercised in May 2018.

In conjunction with the YDKN acquisition on March 11, 2017, the warrant issued by YDKN to the UST under the CPP has been converted into a warrant to purchase up to 207,320 shares of our common stock at an exercise price of $9.63 per share. Subsequent adjustments related to actual dividends paid by us have increased the share amount of these warrants to 225,439, with a resulting lower exercise price of $8.86 per share as of June 30, 2019. The warrant, which was recorded at its fair value on March 11, 2017, was sold at auction by the UST and was exercised prior to expiring in July 2019.