Yes, so long as you bring the minimum HQ and 2 Troops per standard detachment (in a normal army) you can field as many detachments as you want in the allotted points. You don't need, say, 2k points before you bring a second normal detachment.
Every Formation also counts as a detachment, fwiw. You're just plain allowed to bring as many detachments as you like--detachments are the new "structure" around which you build your army, the FOC chart being just one of many options in that regard.
Many tournaments are banning multiple primary detachments--for example, Codex: Knights only allows 1-3 Knights per detachment, so that keeps people from spamming only Knights in a tournament. Also keeps 6 HS or FA lists from being fielded (though often Formations and Allies still allow lopsided, min-maxed lists... which I daresay isn't necessarily a bad thing, if most or all armies have access to similar levels of cheese. ...which they aren't)
What sphinx of plascrete and adamantium bashed open their skulls and ate up their brains and imagination? Imperator! Imperator!