You may check CBP web site for detail.
yBfX4aH:` =kBN&v_(! http://www.cbp.gov $aHHXd}@t2 W;|%)D)y The following is mentioned in U.S. Customs and Border Protection Declaration Form
VI?kbqjo UD ;UdehC Money And Other Monetary
+nL#c{ Instruments
K<MWiB& You may bring into or take out of the country, including
%#E$wz by mail, as much money as you wish. However, if
{pC$jd>T it is more than $10,000, you will need to report it to
>FqU=Q CBP. Ask the CBP officer for the Currency Reporting
[I}xR(a@n Form (FinCen 105). The penalties for non-compliance
TEi1,yc can be severe.
Y-~MkB “Money” means monetary instruments and includes U.S.
!HKW_m^3J or foreign coins currently in circulation, currency, travelers’
*s|'V+1 checks in any form, money orders, and negotiable
zEYQZywc instruments or investment securities in bearer form.