Under our various plans, senior and other management employees and nonemployee directors have received nonvested stock and stock units. In conjunction with the acquisition of DIRECTV, restricted stock units issued under DIRECTV plans were converted to AT&T shares. The shares will vest over a period of one to four years in accordance with the terms of those plans. We do not intend to issue any additional grants under the DIRECTV plans. Any future grants will be made under the AT&T plans.

We grant performance stock units, which are nonvested stock units, based upon our stock price at the date of grant and award them in the form of AT&T common stock and cash at the end of a three-year period, subject to the achievement of certain performance goals. We treat the cash portion of these awards as a liability. We grant forfeitable restricted stock and stock units, which are valued at the market price of our common stock at the date of grant and vest typically over a two- to ten-year period. We also grant other nonvested stock units and award them in cash at the end of a three-year period, subject to the achievement of certain market based conditions. As of December 31, 2015, we were authorized to issue up to approximately 109 million shares of common stock (in addition to shares that may be issued upon exercise of outstanding options or upon vesting of performance stock units or other nonvested stock units) to officers, employees and directors pursuant to these various plans.

We account for our share-based payment arrangements based on the fair value of the awards on their respective grant date, which may affect our ability to fully realize the value shown on our consolidated balance sheets of deferred tax assets associated with compensation expense. We record a valuation allowance when our future taxable income is not expected to be sufficient to recover the asset. Accordingly, there can be no assurance that the current stock price of our common shares will rise to levels sufficient to realize the entire tax benefit currently reflected on our consolidated balance sheets. However, to the extent we generate excess tax benefits (i.e., that additional tax benefits in excess of the deferred taxes associated with compensation expense previously recognized) the potential future impact on income would be reduced.

The compensation cost recognized for those plans was included in operating expenses in our consolidated statements of income, as reflected in the table below. The total income tax benefit recognized in the consolidated statements of income for share-based payment arrangements was $172 for 2015, compared to $122 for 2014 and $175 for 2013.

		2015		2014		2013
Performance stock units	$	299	$	226	$	381
Restricted stock and stock units		147		93		80
Other nonvested stock units		5		(1)		(3)
Total	$	451	$	318	$	458

A summary of the status of our nonvested stock units as of December 31, 2015, and changes during the year then ended is presented as follows (shares in millions):

Nonvested Stock Units	Shares		Weighted-Average Grant-Date Fair Value
Nonvested at January 1, 2015	26	$	33.52
Granted	14		33.98
Issued in DIRECTV acquisition	11		34.29
Vested	(13)		33.86
Forfeited	(2)		34.07
Nonvested at December 31, 2015	36	$	33.78

As of December 31, 2015, there was $563 of total unrecognized compensation cost related to nonvested share-based payment arrangements granted. That cost is expected to be recognized over a weighted-average period of 2.15 years. The total fair value of shares vested during the year was $450 for 2015, compared to $327 for 2014 and $336 for 2013.

It is our policy to satisfy share option exercises using our treasury stock. Cash received from stock option exercises was $46 for 2015, $43 for 2014 and $135 for 2013.