In 2015, the Company adopted and the shareholders approved the 2015 Omnibus Incentive Plan (2015 Plan), which replaced the 2005 Stock Incentive Plan (2005 Plan). The 2015 Plan provides the Company the ability to grant equity awards to officers, directors, employees and consultants, including, but not limited to, nonqualified or incentive stock options, restricted stock awards, restricted stock units and deferred restricted stock units at a price based on the date of the grant. The Company typically issues new shares upon exercise of stock options and vesting of other equity awards.

Under the 2015 Plan, the remaining unissued authorized shares of the 2005 Plan that are not subject to outstanding awards thereunder were authorized for issuance. Additionally, any shares that had been awarded but remained unissued under the 2005 Plan that were subsequently canceled, forfeited, or reacquired by the Company would be authorized for issuance under the 2015 Plan. As of December 31, 2019, 6.9 million shares were available for grant under the 2015 Plan.

The Company recognized $53 million, $46 million and $41 million in share-based compensation expense for the years ended December 31, 2019, 2018 and 2017, respectively. Total unrecognized compensation expense related to non-vested restricted stock awards, restricted stock units, and performance share units was $46 million as of December 31, 2019. This cost is expected to be recognized over a weighted-average period of 1.6 years.

Through 2011, the Company issued options to directors and to certain of the Company's officers and employees. Options generally vested ratably over a two- to four-year period from the date of grant and expired within seven to ten years from the date of grant. Certain options provide for accelerated vesting upon a change of control. The Company measures compensation expense based on the exercise price which is equal to the fair value of the shares on the grant date.

The Company issues restricted stock awards to directors. Restricted stock awards are issued at the fair value on the date of grant and vest one year from the date of issuance. At December 31, 2019 there were less than 0.1 million restricted stock awards outstanding. Non-employee directors may also elect to defer all or a portion of their cash and equity compensation into deferred restricted stock units.

The Company issues restricted stock units to certain of the Company's officers and employees. Each restricted stock unit can be converted into one share of the Company’s common stock upon vesting. These restricted stock units are issued at the fair value on the date of grant and vest ratably over the requisite service period, generally one to four years.

Beginning in 2015, the Company also issued performance share units to certain of the Company’s officers. Each performance share unit can be converted into one share of the Company’s common stock upon vesting. Vesting of performance share units is contingent upon achievement of certain predefined performance targets over the performance period. These performance share units are issued at the fair value on the date of grant. Performance share units granted prior to 2019 vest over three successive one-year performance periods based upon the achievement of performance targets. Beginning in 2019, performance share units vest over a single three-year performance period.

A summary of restricted stock and performance stock unit activity is presented below (shares in thousands):



	Restricted Stock Units				Performance Share Units
	Units		Weighted Average Grant Date Fair Value		Units		Weighted Average Grant Date Fair Value
Outstanding at December 31, 2018	1,987		$	39.87	229		$	47.24
Granted⁽¹⁾	1,053		45.86		180		46.70
Vested⁽¹⁾	(1,050	)	34.53		(142	)	48.66
Forfeited	(85	)	44.80		—		—
Outstanding at December 31, 2019	1,905		44.84		267		46.12

Expected to vest at December 31, 2019	1,859		44.80

The total fair value of restricted stock awards, restricted stock units and performance share units that vested was $56 million, $76 million and $58 million during the years ended December 31, 2019, 2018 and 2017, respectively.

On the date that the Company pays a common stock dividend, holders of restricted stock units, deferred restricted stock units and performance stock units are granted dividend equivalent units which are forfeitable and are subject to the same vesting terms as the stock units with respect to which they have been awarded. The amount of such dividend equivalent units are not material to the year ended December 31, 2019 or December 31, 2018 and are included in the number of shares granted.

In May 2018, the shareholders of the Company approved the 2018 Employee Stock Purchase Plan (2018 ESP Plan), and reserved 4.0 million shares of common stock for sale to employees at a price no less than 85% of the fair market value per share of the common stock on the purchase date. The Company currently offers six month enrollment periods at the end of which employees can purchase shares of the Company's common stock at a price equal to 95% of the closing market price on the date of purchase. The initial offering period began on September 1, 2018. No share-based compensation expense was recorded in connection with the 2018 ESP Plan as it was deemed non-compensatory. Employees purchased 90,348 shares under the plan during the year ended December 31, 2019.

The Company has a 401(k) salary deferral program for eligible employees who have met certain service requirements. The Company matches certain employee contributions; additional contributions to this plan are at the discretion of the Company. Total contribution expense under this plan was $21 million, $19 million and $11 million for the years ended December 31, 2019, 2018, and 2017 respectively.