Based on
http://www.westegg.com/inflation/ (which cites Consumer Price Index statistics from Historical Statistics of the United States and the annual editions of Statistical Abstracts of the United States for inflation conversion)
and
http://the.honoluluadvertiser.com/peaceinthepacific/numbers (which cites the National D-Day museum for war costs),
I calculate that 3 trillion in 2010 dollars is about 86% of what was spent by the US to fight WWII (converting the 2010 dollars to 1945 dollars).
Note that according to that website about WWII costs, our costs were nearly as much as Japan, Britain, France, and the Soviet Union combined.
Thanks for that calculation on the comparison with WWII.