My sister and her husband use their passports for ID regardless of where they are going, even if just flying from Florida to South Carolina. At first I thought it was overkill when she told me, but then her logic is flawless. "Why constantly wonder what the current rules are and what you can get by with? We don't have to worry if we just use the passports since they will always be accepted". You really can't argue with that statement, even though a license is good for U.S. flights.