In 2005 the DOD spent 19% of the 2.5 trillion Federal Budget. 474 Billion vs 2.472 in outlays. Plus emergency funds for Afgan and Iraq.
We spend a lot on national defense through the intelligence agencies, many of which are not funded through DOD. Then there's the Dept. of Homeland Buffoonery.  Also, the absurdity in Iraq has repeatedly been funded through special appropriations that are not part of DOD's budget. My guess is that we are spending at least $650-750 billion/year on national defense.