STOCKHOLDERS' EQUITY

Equity-Based Incentive Plans

Our 2009 Equity Incentive Plan (the 2009 Plan) provides for the grant of stock awards, including stock options, RSUs, RSAs, and other stock awards. Shares available for grant as of December 31, 2018 were 12 million.

Stock Options

Stock options are granted to employees under the 2009 Plan at exercise prices equal to the fair market value of our common stock on the dates of grant. Options generally have a maximum contractual term of 10 years. Options are generally vested over four years, based on continued service. Stock options are forfeited if the employee ceases to be employed by us prior to vesting.

The following table summarizes stock option activity under our equity-based plan for the year ended December 31, 2018:



	Number of Shares		Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in millions)
Balance at December 31, 2017	1,296,863		$	12.27	5.87	$	41
Exercised	(617,157	)	11.00
Forfeited	(15,694	)	32.81
Canceled	(8,497	)	32.02
Balance at December 31, 2018	655,515		$	12.90	4.91	$	19
Exercisable at December 31, 2018	642,631		$	12.65	4.94	$	19
Vested and expected to vest at December 31, 2018	655,515		$	12.90	4.91	$	19



	Year Ended December 31,
Additional Disclosures for Stock Options (in millions)	2018		2017		2016
Total fair value of options vested	$	4	$	7	$	7
Total intrinsic value of options exercised	24		36		21
Cash received from options exercised	7		11		5

Restricted Stock Units and Restricted Stock Awards

In 2018, the Company granted time-based and performance-based restricted stock awards to the Company's named executive officers. A recipient of RSAs owns the underlying shares of common stock upon grant and some of the benefits of ownership, such as voting and dividend rights, but the recipient may not sell those shares and realize any value on a sale, until all time-based and performance-based restrictions have been satisfied or lapsed.

Time-based RSUs and RSAs generally vest over a four-year term. Performance-based RSUs and RSAs are subject to vesting requirements based on certain financial performance metrics as defined in the grant notice. Actual number of shares earned may range from 0% to 200% of the target award. Awards granted in 2017 and 2018 are based on single-year performance period subject to subsequent multi-year vesting with 50% of the shares earned will vest in one year after the performance period and the remaining shares in the year after.

Compensation expense is recognized ratably over the vesting period based on the probability of the number of awards expected to vest at each reporting date.

The following table summarizes RSU and RSA activity under our equity-based plans for the year ended December 31, 2018:



	RSUs				RSAs
	Number of Units		Weighted-Average Grant Date Fair Value		Number of Shares		Weighted-Average Grant Date Fair Value
Nonvested at December 31, 2017	2,703,335		$	25.82	—		$	—
Granted	714,358		47.07		372,783		49.02
Vested	(1,273,796	)	27.26		(13,683	)	47.61
Forfeited	(406,343	)	28.68		(12,308	)	47.61
Nonvested at December 31, 2018	1,737,554		$	32.83	346,792		$	49.13



	RSUs						RSAs
	Year Ended December 31,						Year Ended December 31,
Additional Disclosures for equity-based plans	2018		2017		2016		2018		2017		2016
Total grant date fair value of shares granted (in millions)	$	34	$	46	$	42	$	18	$	—	$	—
Total grant date fair value of shares vested (in millions)	$	35	$	21	$	16	$	1	$	—	$	—
Shares withheld to settle payroll tax liabilities related to vesting of shares held by employees	451,875		335,101		217,769		6,357		—		—

Employee Stock Purchase Plan

Our 2014 Employee Stock Purchase plan (ESPP) offers eligible employees an option to purchase shares of our common stock through a payroll deduction. The purchase price is equal to the lesser of 85% of the fair market value of our common stock on the offering date or 85% of the fair market value of our common stock on the applicable purchase date. Offering periods are approximately six months in duration and will end on or about May 15 and November 15 of each year. Employees may contribute a minimum of 1% and a maximum of 15% of their earnings. The plan is considered to be a compensatory plan. We issued 175,966, 224,928, and 283,644 shares under the ESPP during 2018, 2017, and 2016, respectively. As of December 31, 2018, approximately 3 million shares were reserved for future issuances under the ESPP.

Equity-Based Compensation



	ESPP Assumptions
Year Ended December 31,	Expected Term (in Years)	Expected Volatility	Risk-Free Interest Rate	Expected Dividend Yield
2018	0.50	27-37%	1.42-2.5%	0	%
2017	0.50	28-37%	0.62-1.42%	0	%
2016	0.50	32-76%	0.33-0.62%	0	%

Stock-based compensation expense and other disclosures for stock-based awards made to our employees pursuant to the equity plans was as follows:



	Year Ended December 31,
(in millions)	2018		2017		2016
Cost of providing services	$	10	$	8	$	7
Sales and marketing	8		6		6
General and administrative	22		14		11
Systems development and programming costs	4		4		2
Total stock-based compensation expense	$	44	$	32	$	26
Income tax benefit related to stock-based compensation expense	$	11	$	7	$	9
Tax benefit realized from stock options exercised and similar awards	$	23	$	28	$	7

The table below summarizes unrecognized compensation expense for the year ended December 31, 2018 associated with the following:



	Amount (in millions)		Weighted-Average Period (in Years)
Nonvested stock options	$	—	0.11
Nonvested RSUs	49		2.07
Nonvested RSAs	12		2.44

Stock Repurchases

During 2018, the board of directors did not authorize additional repurchases. During 2017 and 2016, the board of directors authorized $120 million and $100 million, respectively, of outstanding common stock to be repurchased with no expiration from the date of authorization. As of December 31, 2018, approximately $75 million remained available for repurchase pursuant to our stock repurchase program. During 2018, 2017, and 2016, we repurchased 1,190,995 shares, 1,549,434 shares and 3,414,675 shares, respectively.

On February 6, 2019, our board of directors authorized a $300 million incremental increase to our ongoing stock repurchase program initiated in May 2014.