I have the 2012 CBO report:
[P7] In 2011, defense outlays totaled $700 billion, an increase of $11 billion, or less than 2 percent—well below the 9 percent average annual growth rate recorded over the previous 10 years. Modest increases in spending for operations and maintenance and for military personnel were partially offset by reductions elsewhere, primarily in procurement. Defense outlays will fall by $20 billion (or 3 percent) in 2012, CBO projects, largely because of a reduction in spending for military operations in Afghanistan and Iraq.
[p17] In 2011, CBO estimates, the number of U.S. active-duty, Reserve, and National Guard personnel deployed for war related activities averaged about 195,000. Under the scenario shown in Table 1-6, the average number of military personnel deployed for war-related purposes would decline over four years: from 115,000 in 2012 to 85,000 in 2013, 60,000 in 2014, and 45,000 in 2015 and thereafter. (Those numbers could represent various allocations of forces among Afghanistan and other regions.) Under that scenario, and assuming that the related funding for diplomatic operations and foreign aid declines at a similar rate, total discretionary outlays over the 2013–2022 period would be $838 billion less than the amount in the baseline.
So CBO doesn't assume complete troop withdrawel, at least not in 2011. Actually, on p70, there is a whole box related to the war spending (too big to cut and paste here), you might wanna get to that. Apparently they have some problems isolating the spending on Irak and Afghanistan:
Because most appropriations for operations in Afghanistan and Iraq and for related activities appear in the same budget accounts as appropriations for DoD’s other functions, it is impossible to determine precisely how much has been spent on those activities.