Share-Based Compensation Plans

The following table summarizes share-based compensation expense recognized in the Condensed Consolidated Statements of Income in Compensation and benefits (in millions):



	Three months ended March 31
	2018		2017
Restricted share units (“RSUs”)	$	58	$	55
Performance share awards (“PSAs”)	16		19
Employee share purchase plans	3		4
Total share-based compensation expense	$	77	$	78

Restricted Share Units

RSUs generally vest between three and five years. The fair value of RSUs is based upon the market value of Aon plc ordinary shares at the date of grant. With certain limited exceptions, any break in continuous employment will cause the forfeiture of all non-vested awards. Compensation expense associated with RSUs is recognized on a straight-line basis over the requisite service period. Dividend equivalents are paid on certain RSUs, based on the initial grant amount.

The following table summarizes the status of the Company’s RSUs, including shares related to the Divested Business (shares in thousands, except fair value):



	2018				2017
	Shares		Fair Value at Date of Grant		Shares		Fair Value at Date of Grant
Non-vested at beginning of period	4,849		$	104	6,195		$	89
Granted	505		144		614		119
Vested	(806	)	101		(960	)	90
Forfeited	(63	)	105		(50	)	91
Non-vested at end of period	4,485		$	109	5,799		$	92

Unamortized deferred compensation expense amounted to $352 million as of March 31, 2018, with a remaining weighted-average amortization period of approximately 2.0 years.

Performance Share Awards

The vesting of PSAs is contingent upon meeting a cumulative level of earnings per share related performance over a three-year period. The actual issue of shares may range from 0-200% of the target number of PSAs granted, based on the terms of the plan and level of achievement of the related performance target. The grant date fair value of PSAs is based upon the market price of Aon plc ordinary shares at the date of grant. The performance conditions are not considered in the determination of the grant date fair value for these awards. Compensation expense is recognized over the performance period based on management’s estimate of the number of units expected to vest. Management evaluates its estimate of the actual number of shares expected to be issued at the end of the programs on a quarterly basis. The cumulative effect of the change in estimate is recognized in the period of change as an adjustment to Compensation and benefits in the Condensed Consolidated Statements of Income, if necessary. Dividend equivalents are not paid on PSAs.

Information as of March 31, 2018 regarding the Company’s target PSAs granted and shares that would be issued at current performance levels for PSAs granted during the three months ended March 31, 2018 and the years ended December 31, 2017 and 2016, respectively, is as follows (shares in thousands and dollars in millions, except fair value):



	March 31, 2018		December 31, 2017		December 31, 2016
Target PSAs granted during period	561		548		750
Weighted average fair value per share at date of grant	$	135	$	114	$	100
Number of shares that would be issued based on current performance levels	561		942		745
Unamortized expense, based on current performance levels	$	75	$	68	$	19