The 24hr volume for bitcoin is currently at 6.2 B.
Selling 10 MM of bitcoin in a day would not affect price very much. Looking at the largest American exchange (6% of daily btc volume), GDAX, a 10 MM market sell order would drop the price to around 9400 USD from 9750 USD currently.
Selling 100 MM of bitcoin in a day would affect the price significantly. Looking at GDAX, a 100 MM market sell order would drop the price to around 7000 USD from 9750 USD currently. Although this would be arbed pretty quickly and I would think that it would recover to maybe 8500 USD.