F9 3990 then DL 16 at Detroit
Dallas-Fort Worth → Detroit → London
Timetable, Detroit time
21:43F9 3990 from Dallas-Fort Worth at the gate
19:15DL 16 to London leaves the gate
21 h 32 apart on the timetable, overnight
DL 16 leaves 21 h 32 after F9 3990 arrives on the timetable: more than half a day, so not a connection we count.