material impact on the service cost and interest cost components of net periodic benefit costs for a 1% ( 1 % ) change in the assumed health care trend rate . for most of the participants in the u.s . plan , aon 2019s liability for future plan cost increases for pre-65 and medical supplement plan coverage is limited to 5% ( 5 % ) per annum . because of this cap , net employer trend rates for these plans are effectively limited to 5% ( 5 % ) per year in the future . during 2007 , aon recognized a plan amendment which phases out post-65 retiree coverage in its u.s . plan over the next three years . the impact of this amendment on net periodic benefit cost is being recognized over the average remaining service life of the employees . 14 . stock compensation plans the following table summarizes stock-based compensation expense recognized in continuing operations in the consolidated statements of income in compensation and benefits ( in millions ) : .

1	years ended december 31	2010	2009	2008
2	rsus	$ 138	$ 124	$ 132
3	performance plans	62	60	67
4	stock options	17	21	24
5	employee stock purchase plans	4	4	3
6	total stock-based compensation expense	221	209	226
7	tax benefit	75	68	82
8	stock-based compensation expense net of tax	$ 146	$ 141	$ 144

during 2009 , the company converted its stock administration system to a new service provider . in connection with this conversion , a reconciliation of the methodologies and estimates utilized was performed , which resulted in a $ 12 million reduction of expense for the year ended december 31 , 2009 . stock awards stock awards , in the form of rsus , are granted to certain employees and consist of both performance-based and service-based rsus . service-based awards generally vest between three and ten years from the date of grant . the fair value of service-based awards is based upon the market value of the underlying common stock at the date of grant . with certain limited exceptions , any break in continuous employment will cause the forfeiture of all unvested awards . compensation expense associated with stock awards is recognized over the service period . dividend equivalents are paid on certain service-based rsus , based on the initial grant amount . performance-based rsus have been granted to certain employees . vesting of these awards is contingent upon meeting various individual , divisional or company-wide performance conditions , including revenue generation or growth in revenue , pretax income or earnings per share over a one- to five-year period . the performance conditions are not considered in the determination of the grant date fair value for these awards . the fair value of performance-based awards is based upon the market price of the underlying common stock at the date of grant . compensation expense is recognized over the performance period , and in certain cases an additional vesting period , based on management 2019s estimate of the number of units expected to vest . compensation expense is adjusted to reflect the actual number of shares paid out at the end of the programs . the actual payout of shares under these performance- based plans may range from 0-200% ( 0-200 % ) of the number of units granted , based on the plan . dividend equivalents are generally not paid on the performance-based rsus . during 2010 , the company granted approximately 1.6 million shares in connection with the completion of the 2007 leadership performance plan ( 2018 2018lpp 2019 2019 ) cycle and 84000 shares related to other performance plans . during 2010 , 2009 and 2008 , the company granted approximately 3.5 million .

Question: what was the difference in total stock-based compensation expense between 2009 and 2010?
Answer: 12