The components of the FAS/CAS Pension Adjustment were as follows:
Three Months Ended Six Months Ended (In millions) Jun 30, 2013 Jul 1, 2012 Jun 30, 2013 Jul 1, 2012 FAS expense
$ (319 ) $ (281 ) $ (637 ) $ (562 )CAS expense 246 211 492 422 FAS/CAS Pension Adjustment $ (73 ) $ (70 ) $ (145 ) $ (140 )A key driver of the difference between FAS and CAS expense (and consequently, the FAS/CAS Pension Adjustment) is the pattern of earnings and expense recognition for gains and losses that arise when our asset and liability experience differ from our assumptions under each set of requirements. Generally, such gains or losses are amortized under FAS over the average future working lifetime of the eligible employee population of approximately 10 years at June 30, 2013and December 31, 2012, and are currently amortized under CAS over a 15-year period. However, the CAS Harmonization will reduce this amortization period from 15 to 10 years beginning in 2013, as well as changing the liability measurement method. We do not utilize a "corridor" method under FAS to determine the deferred actuarial losses that are subject to amortization for our U.S. pension plans. In accordance with both FAS and CAS, a "calculated market-related value" of our plan assets is used to calculate the amount of deferred asset gains or losses to be amortized. The market-related value of assets is determined using actual asset gains or losses over a certain prior period (three years for FAS and five years for CAS, subject to certain limitations under CAS on the difference between the market-related value and actual market value of assets). Because of this difference in the number of years over which actual asset gains or losses are recognized and subsequently amortized, FAS expense generally tends to reflect recent gains or losses faster than CAS. Another driver of CAS expense (but not FAS expense) is the funded status of our pension plans under CAS. As noted above, CAS expense is only recognized for plans that are not fully funded; consequently, if plans become or cease to be fully funded under CAS due to our asset or liability experience, our CAS expense will change accordingly. The increase in our FAS/CAS Pension Adjustment of $3 millionin the second quarter of 2013 compared to the second quarter of 2012 was driven by a $38 millionincrease in our FAS expense offset by a $35 millionincrease in our CAS expense. The increase in our FAS/CAS Pension Adjustment of $5 millionin the first six months of 2013 compared to the first six months of 2012 was driven by a $75 millionincrease in our FAS expense offset by a $70 millionincrease in our CAS expense. The increase in our FAS expense in the second quarter and first six months of 2013 was due primarily to the increase in the amortization of deferred actuarial losses as a result of the decrease in the discount rate. The increase in the CAS expense in the second quarter and first six months of 2013 was primarily due to the continued recognition of the 2008 negative asset returns.