The USA’s Central Bank is the Federal Reserve.
https://www.federalreserve.gov/
Run by the New Yorker, Janet Yellan
https://en.wikipedia.org/wiki/Janet_Yellen
The Growth in the Federal Reserve’s balance sheet since 2007 when the Global Financial Crisis began is best documented here:-
https://www.federalreserve.gov/monetarypolicy/bst_recenttrends.htm
Total assets today are at over $4,470 Billion (That is $4.470 TRILLION).
Looking at that graph:
10th Sept 2007: Assets = $886,314 MILLION
22nd May 2017: Assets = $4,470,852 MILLION
One can see the US Fed buying the bad assets of the troubled banks = TARP The Troubled Asset Relief Programme.