Our 2019 Equity Incentive Plan (the 2019 Plan), approved in May 2019, provides for the grant of stock awards, including stock options, RSUs, RSAs, and other stock awards. Shares available for grant as of December 31, 2019 was approximately 3 million.

The 2009 Equity Incentive Plan (the 2009 Plan), was terminated, replaced and superseded by the 2019 Plan, except that any outstanding awards granted under the 2009 Plan remain in effect pursuant to their terms.

Stock options are granted to employees at exercise prices equal to the fair market value of our common stock on the dates of grant. Stock options generally have a maximum contractual term of 10 years. Stock options generally vest over 4 years, and are generally forfeited if the employee terminates service prior to vesting.



	Number of Shares		Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in millions)
Balance at December 31, 2018	655,515		$	12.90	4.91	$	19
Exercised	(187,504	)	10.80
Expired	(6,000	)	0.50
Balance at December 31, 2019	462,011		$	13.90	4.02	$	20
Exercisable at December 31, 2019	462,011		$	13.90	4.02	$	20
Vested and expected to vest at December 31, 2019	462,011		$	13.90	4.02	$	20



	Year Ended December 31,
Additional Disclosures for Stock Options (in millions)	2019		2018		2017
Total fair value of options vested	$	1	$	4	$	7
Total intrinsic value of options exercised	9		24		36
Cash received from options exercised	2		7		11

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 2019 and 2018 are based on a single-year performance period subject to subsequent multi-year vesting with 50% of the shares earned vesting in one year after the performance period and the remaining shares in the year after. RSUs and RSAs are generally forfeited if the participant terminates service prior to vesting.



	Time-based RSUs and RSAs
	Total Number of RSUs		Total Number of RSAs		Total Number of Shares		Weighted-Average Grant Date Fair Value
Nonvested at December 31, 2018	1,560,685		98,445		1,659,130		$	33.88
Granted	616,224		—		616,224		60.99
Vested	(891,633	)	(37,309	)	(928,942	)	32.53
Forfeited	(180,547	)	—		(180,547	)	38.89
Nonvested at December 31, 2019	1,104,729		61,136		1,165,865		$	48.47



	Performance-based RSUs and RSAs
	Total Number of RSUs		Total Number of RSAs		Total Number Shares		Weighted-Average Grant Date Fair Value
Nonvested at December 31, 2018	176,869		248,347		425,216		$	42.02
Granted	83,110		—		83,110		59.83
Vested	(155,589	)	(122,387	)	(277,976	)	39.45
Cancelled	(61,400	)	—		(61,400	)	61.75
Forfeited	(27,238	)	(11,103	)	(38,341	)	41.52
Nonvested at December 31, 2019	15,752		114,857		130,609		$	49.70



	Time-based RSUs and RSAs
	Year Ended December 31,
Additional Disclosures for equity-based plans	2019		2018		2017
Total grant date fair value of shares granted (in millions)	$	38	$	38	$	37
Total grant date fair value of shares vested (in millions)	$	30	$	28	$	21
Shares withheld to settle payroll tax liabilities related to vesting of shares held by employees	315,762		348,010		332,857



	Performance-based RSUs and RSAs
	Year Ended December 31,
Additional Disclosures for equity-based plans	2019		2018		2017
Total grant date fair value of shares granted (in millions)	$	4	$	14	$	10
Total grant date fair value of shares vested (in millions)	$	11	$	7	$	—
Shares withheld to settle payroll tax liabilities related to vesting of shares held by employees	135,877		110,222		2,244

Our 2014 Employee Stock Purchase plan (ESPP) offers eligible employees an option to purchase shares of our common stock through payroll deductions. 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. The plan is considered to be a compensatory plan. As of December 31, 2019, approximately 3 million shares were reserved for future issuances under the ESPP.

In applying the Black Scholes option valuation model for the ESPP options, we use the following assumptions:



	Year Ended December 31,
(in millions)	2019		2018		2017
Expected Term (in Years)	0.5		0.5		0.5
Expected Volatility	27-42%		27-37%		28-37%
Risk-Free Interest Rate	1.6-2.5%		1.42-2.5%		0.62-1.42%
Expected Dividend Yield	0	%	0	%	0	%

Shares Issued under ESPP	207,324		175,966		224,928

Stock based compensation expense is measured based on the fair value of the stock award on the grant date and recognized over the requisite service period for each separately vesting portion of the stock award. 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)	2019		2018		2017
Cost of providing services	$	8	$	10	$	8
Sales and marketing	3		8		6
General and administrative	28		22		14
Systems development and programming costs	2		4		4
Total stock based compensation expense	$	41	$	44	$	32
Total stock based compensation capitalized	$	1	$	—	$	—
Income tax benefit related to stock based compensation expense	$	11	$	11	$	7
Tax benefit realized from stock options exercised and similar awards	$	18	$	23	$	28

The table below summarizes unrecognized compensation expense for the year ended December 31, 2019 associated with the following:



	Amount (in millions)		Weighted-Average Period (in Years)
Nonvested stock options	$	—	0
Nonvested RSUs	51		2.27
Nonvested RSAs	2		0.49