Bottom of the page on baggage allowances:

"All customers flying in First or Business Class will receive up to three checked bags, up to 70 pounds each, for free. SkyMiles Medallion members and WorldPerks Elite members flying in Coach Class will receive up to two checked bags, up to 70 pounds each, for free."

I often travel with heavy bags for my work. When I travel with others who are FF, sometimes the agent lets them check 50+ pound bags as well, sometimes not.