It is becoming increasingly common for US retail brokerages to let customers hold foreign currencies. Sometimes this is done as an outright currency investment, and other times it is a byproduct of buying or selling a foreign stock. Interactive Brokers in the US was the first to pioneer this, and Schwab and others are following their lead. This raises the interesting question what is the capital gain/tax treatment of holding a foreign currency, if you take a gain or loss going from and to US dollars?
Brokers create a 1099 at the time you sell a foreign stock. They use USD value at time of purchase as the cost basis, and USD value of the stock at time of sale as the value to calculate gain or loss. These stock values in USD are what goes on the broker's 1099-B.
Apparently the brokers do not record capital gains information for pure currency holdings in a 1099. Calculating it on your own is next to impossible. How can you distinguish Canadian dollars held that were converted from USD and held as Canadian dollars forever, from some subset of that currency that ended up buying and selling some Canadian stock multiple times ? Keeping track of when the currency was being held as part of a stock investment and when it was part of a currency holding, would be a horrificly complex reconciliation to perform. What are tax reporting rules regarding currencies?