I did this achievememnt last, but you can do it anytime on any single race event.
Your settings should be:
Turn Damage Off
Laps - 20 (30 if yo need the extra help)
Racers - 1
Traffic - Rush Hour
Keep running laps around damaging everything in your way. I think building your combo meter is the fastest way. I was getting about 300k before I had to reset my vehicle. Keep doing this until you reach 10,000,000 the achievement will unlock on the spot!!
You can quit out or let the cpu beat you in the race (it will take some time), but it will save at the end of your damage and it will apply to your 10 billion damage for the other achievement