Moon, Jupiter, Mercury and Venus are Natural Benefics.
Sun, Mars, Saturn, Rahu, and Ketu are Natural Malefics.
Sun Dasha is 6 years
Moon Dasha is 10 years
Mars Dasha is 7 years
Rahu Dasha is 18 years
Jupiter Dasha is 16 years
Saturn Dasha is 19 years
Mercury Dasha is 17 years
Ketu Dasha is 7 years
Venus Dasha is 20 years
These are called Mahadasas