I understand that the balance of payments should be equal, and that the Current Account should equal the Capital Account. The U.S. imports more than it exports, so other countries have more of our currency and can use it to buy assets. What I don't understand is how that USD is categorized in the interim. If Company U.S. buys $1 million worth of goods from Company China, how is that cash categorized while it remains unspent in Company China's bank account? What if they just let it sit there and continue to save that cash, wouldn't this throw off the balance of payments and cause the Current Account to be greater than the Capital Account due to the unspent cash?
The balance of payments accounts are maintained on a double entry basis. An import of $1 million will show as a negative $1 million entry in the Current Account. When the Chinese exporter receives and deposits this $1 million check in its Chinese bank, the latter has now a claim of $1 million on a US bank deposit. It is export of assets and will show as $1 million positive entry in the Financial Account of Balance of Payments.
As a result, the balance of payment identity, that is, Current Account + Capital Account = 0, holds.