I created the above graph in Fred. It is slightly out of scale as it's in dollars, euros, and 100 million Yen. There are about 1.16 dollars per euro and .92 dollars per 100 yen.
I was going to download the data into Excel to equalize things but before I did, I searched for "central bank balance sheets assets as percentage of GDP" and came across Global Economic Briefing: Central Bank Balance Sheets, released today by Dr. Edward Yardeni.
It's a treasure trove of charts.
Assets of Major Central Banks in US Dollars by Country
Major Central Bank Assets Combined US Dollar Total
Yearly Change in Central Bank Assets
Yardeni posted 16 charts in all. Inquiring minds may wish to give it a closer look.
Mike "Mish" Shedlock