
13.	STOCK-BASED COMPENSATION

Overview

Under our 2011 Omnibus Stock Incentive Plan (the OSIP), various stock and stock-based awards may be granted to employees and non-employee directors. Awards available under the OSIP include options to purchase shares of common stock, performance awards that vest upon the achievement of an objective performance goal, stock appreciation rights, restricted stock that vests over a period determined by our compensation committee, and dividend equivalent rights (DERs). The OSIP was approved by our stockholders on April 28, 2011 and re-approved by our stockholders on May 12, 2016. As of December 31, 2017, 9,409,188 shares of our common stock remained available to be awarded under the OSIP.

We also maintain other stock-based compensation plans under which previously granted equity awards remain outstanding. No additional grants may be awarded under these plans.

The following table reflects activity related to our stock-based compensation arrangements (in millions):



	Year Ended December 31,
	2017		2016		2015
Stock-based compensation expense:
Restricted stock	$	58	$	52	$	47
Performance awards	19		15		11
Stock options	—		1		1
Total stock-based compensation expense	$	77	$	68	$	59
Tax benefit recognized on stock-based compensation expense	$	27	$	24	$	21
Tax benefit realized for tax deductions resulting from exercises and vestings	44		33		66
Effect of tax deductions in excess of recognized stock-based compensation expense (a)	24		22		44

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(a)	Effective January 1, 2016, the effect of tax deductions in excess of recognized stock-based compensation expense is reported as an operating cash flow. These amounts were previously reported as financing cash flows.

Our significant stock-based compensation arrangement is discussed below.

Restricted Stock

Restricted stock is granted to employees and non-employee directors. Restricted stock granted to employees vests in accordance with individual written agreements between the participants and us, usually in equal annual installments over a period of three years beginning one year after the date of grant. Restricted stock granted to our non-employee directors vests in equal annual installments over a period of three years beginning one year after the date of grant. The fair value of each restricted stock per share is equal to the market price of our common stock. A summary of the status of our restricted stock awards is presented in the following table.



	Number of Shares		Weighted- Average Grant-Date Fair Value Per Share
Nonvested shares as of January 1, 2017	1,566,950		$	60.68
Granted	739,393		79.32
Vested	(897,246	)	61.76
Forfeited	(8,057	)	61.22
Nonvested shares as of December 31, 2017	1,401,040		69.82

As of December 31, 2017, there was $61 million of unrecognized compensation cost related to outstanding unvested restricted stock awards, which is expected to be recognized over a weighted-average period of approximately two years.

The following table reflects activity related to our restricted stock (in millions, except per share data):



	Year Ended December 31,
	2017		2016		2015
Weighted-average grant-date fair value per share of restricted stock granted	$	79.32	$	59.00	$	70.07
Fair value of restricted stock vested	71		46		69