After winning at home, the Steelers traveled to Detroit to take on the Lions. The Steelers would score first when Chris Boswell nailed a 34-yard field goal to make the score 3-0. The Lions tied the game up later on when Matt Prater kicked a 48-yard field goal to make it 3-3. The Lions moved into the lead when Prater kicked a 37-yard field goal to make it 6-3. The Steelers moved back into the lead when Le'Veon Bell ran for a 5-yard touchdown to make it 10-6. The Lions retook the lead when Prater kicked 2 more field goals from 51 and 34 yards out to make the score 10-9 and then move up 12-10 at halftime. In the third quarter, it was all Steelers as they retook the lead when Chris Boswell kicked a 38-yard field goal to make it 13-12. Later on in the quarter, Ben Roethlisberger connected with JuJu Smith-Schuster for a 97-yard pass making it 20-12. The Lions scored their only points of the second half in the fourth quarter when Prater kicked a 19-yard field goal to make it 20-15. This would eventually be the final score of the game. With the win, the Steelers went into their bye week 6-2. After falling behind in the all-time series to the Lions 4-12-1 through 1965, the Steelers' victory moved them to 13-2 against Detroit since 1966. The team also held an opponent without a touchdown on the road for the first time since their 28-12 victory over the Browns in 2015.
Question: How many points were the Lions ahead by at the end of the first half?
Answer: 2