institutions . international paper continually monitors its positions with and the credit quality of these financial institutions and does not expect non- performance by the counterparties . note 14 capital stock the authorized capital stock at both december 31 , 2006 and 2005 , consisted of 990850000 shares of common stock , $ 1 par value ; 400000 shares of cumulative $ 4 preferred stock , without par value ( stated value $ 100 per share ) ; and 8750000 shares of serial preferred stock , $ 1 par value . the serial preferred stock is issuable in one or more series by the board of directors without further shareholder action . in july 2006 , in connection with the planned use of projected proceeds from the company 2019s trans- formation plan , international paper 2019s board of direc- tors authorized a share repurchase program to acquire up to $ 3.0 billion of the company 2019s stock . in a modified 201cdutch auction 201d tender offer completed in september 2006 , international paper purchased 38465260 shares of its common stock at a price of $ 36.00 per share , plus costs to acquire the shares , for a total cost of approximately $ 1.4 billion . in addition , in december 2006 , the company purchased an addi- tional 1220558 shares of its common stock in the open market at an average price of $ 33.84 per share , plus costs to acquire the shares , for a total cost of approximately $ 41 million . following the completion of these share repurchases , international paper had approximately 454 million shares of common stock issued and outstanding . note 15 retirement plans u.s . defined benefit plans international paper maintains pension plans that provide retirement benefits to substantially all domestic employees hired prior to july 1 , 2004 . these employees generally are eligible to participate in the plans upon completion of one year of service and attainment of age 21 . employees hired after june 30 , 2004 , who are not eligible for these pension plans receive an additional company contribution to their savings plan ( see 201cother plans 201d on page 83 ) . the plans provide defined benefits based on years of credited service and either final average earnings ( salaried employees ) , hourly job rates or specified benefit rates ( hourly and union employees ) . for its qualified defined benefit pension plan , interna- tional paper makes contributions that are sufficient to fully fund its actuarially determined costs , gen- erally equal to the minimum amounts required by the employee retirement income security act ( erisa ) . in addition , international paper made volun- tary contributions of $ 1.0 billion to the qualified defined benefit plan in 2006 , and does not expect to make any contributions in 2007 . the company also has two unfunded nonqualified defined benefit pension plans : a pension restoration plan available to employees hired prior to july 1 , 2004 that provides retirement benefits based on eligible compensation in excess of limits set by the internal revenue service , and a supplemental retirement plan for senior managers ( serp ) , which is an alternative retirement plan for senior vice presi- dents and above who are designated by the chief executive officer as participants . these nonqualified plans are only funded to the extent of benefits paid , which are expected to be $ 41 million in 2007 . net periodic pension expense service cost is the actuarial present value of benefits attributed by the plans 2019 benefit formula to services rendered by employees during the year . interest cost represents the increase in the projected benefit obli- gation , which is a discounted amount , due to the passage of time . the expected return on plan assets reflects the computed amount of current year earn- ings from the investment of plan assets using an estimated long-term rate of return . net periodic pension expense for qualified and nonqualified u.s . defined benefit plans comprised the following : in millions 2006 2005 2004 .

2006: service cost: 141
interest cost: 506
expected return on plan assets: -540
actuarial loss: 243
amortization of prior service cost: 27
net periodic pension expense ( a ): 377
2005: service cost: 129
interest cost: 474
expected return on plan assets: -556
actuarial loss: 167
amortization of prior service cost: 29
net periodic pension expense ( a ): 243
2004: service cost: 115
interest cost: 467
expected return on plan assets: -592
actuarial loss: 94
amortization of prior service cost: 27
net periodic pension expense ( a ): 111

( a ) excludes $ 9.1 million , $ 6.5 million and $ 3.4 million in 2006 , 2005 and 2004 , respectively , in curtailment losses , and $ 8.7 million , $ 3.6 million and $ 1.4 million in 2006 , 2005 and 2004 , respectively , of termination benefits , in connection with cost reduction programs and facility rationalizations that were recorded in restructuring and other charges in the con- solidated statement of operations . also excludes $ 77.2 million and $ 14.3 million in 2006 and 2005 , respectively , in curtailment losses , and $ 18.6 million and $ 7.6 million of termination bene- fits in 2006 and 2005 , respectively , related to certain divest- itures recorded in net losses on sales and impairments of businesses held for sale in the consolidated statement of oper- ations. .

Questions:
what was the change in the net periodic pension expense from 2005 to 2006?
and what was that net periodic pension expense in 2005?
how much, then, does that change represent in relation to this 2005 net periodic pension expense, in percentage?

Answers:
134
243
55%