Perhaps the main difference between the implementation of Basel II in the United States and the implementation in most other countries is that the U.S. banking agencies plan to retain a revised form of the existing Basel I-based capital rules for the vast majority of U.S. banks; most other countries are replacing Basel I entirely and will apply Basel II to the entire banking system.
Notably, the initial U.S. Basel II proposals, issued in an advance notice of proposed rulemaking (ANPR) in August 2003, suggested that only the advanced approaches be used in the United States; comments on the Basel II ANPR did not indicate any opposition to the agencies' proposed approaches.