Foreign bank deposits at the Federal Reserve have more than doubled to $715 billion from $350 billion since the end of 2010 amid Europe's debt turmoil, buttressing the dollar's status as the world's reserve currency.

Forty-seven non-U.S. banks held balances of more than $1 billion at the New York Fed as of Sept. 30, up from 22 at the end of 2010, according to a survey of 80 financial institutions by ICAP Plc, the world's largest inter-dealer broker. The dollar has appreciated 7.2 percent since Standard & Poor's cut the nation's AAA credit rating Aug. 5, the second-best performance after the yen among developed-nation peers, according to Bloomberg Correlation-Weighted Currency Indexes.

A budget deficit of more than $1 trillion, a deadlock among Congressional supercommittee members on spending cuts and 9 percent unemployment haven't deterred investors from seeking safety in the world's biggest economy. The euro has been undermined by the region's sovereign debt crisis, while the Swiss franc and yen have fallen as their governments buy billions of dollars to weaken them.