From "The ECB's liquidity boost", here first is the background on where in the global central bank central-planning experiment we stand right now:
The ECB President stated in this week's press conference that the ECB's forthcoming programs, i.e. TLTROs coupled with ABS and covered bond purchases, could take the ECB's balance sheet back to early 2012 levels, i.e. to €3tr from €2tr currently. These remarks, not only suggest that the ECB might have a target in mind regarding the size of its balance sheet, but raise questions about the boost to global liquidity from prospective ECB actions.
In aggregate, G4 central balance sheets started rising rapidly from the end of 2010 driven by the Fed's QE2 followed by the BoE's QE, ECB's LTROs, Fed's QE3 and BoJ's QE.