The old rule was "that a complaint should not be dismissed for failure to state a claim unless it appears beyond doubt that the plaintiff can prove no set of facts in support of his claim which would entitled him to relief.” Thus, usually, it was not possible to dismiss a claim for relief on the face of the Complaint.
The official syllabus to the case describes the holding as follows (citations omitted without indication below):
[The] Federal Rule of Civil Procedure requires only “a short and plain statement of the claim showing that the pleader is entitled to relief,” in order to “give the defendant fair notice of what the … claim is and the grounds upon which it rests." While a complaint attacked by a motion to dismiss does not need detailed factual allegations, a plaintiff’s obligation to provide the “grounds” of his “entitle[ment] to relief” requires more than labels and conclusions, and a formulaic recitation of a cause of action’s elements will not do. Factual allegations must be enough to raise a right to relief above the speculative level on the assumption that all of the complaint’s allegations are true. . . . Asking for plausible grounds does not impose a probability requirement at the pleading stage; it simply calls for enough fact to raise a reasonable expectation that discovery will reveal evidence . . . The need at the pleading stage for allegations plausibly suggesting (not merely consistent with) agreement reflects [the] threshold requirement that the “plain statement” possess enough heft to “sho[w] that the pleader is entitled to relief.” . . . The requirement . . . serves the practical purpose of preventing a plaintiff with “ ‘a largely groundless claim’ ” from “ ‘tak[ing] up the time of a number of other people, with the right to do so representing an in terrorem increment of the settlement value.’ ” . . . It is one thing to be cautious before dismissing an antitrust complaint in advance of discovery, but quite another to forget that proceeding to . . . discovery can be expensive. . . . It is no answer to say that a claim just shy of plausible entitlement can be weeded out early in the discovery process, given the common lament that the success of judicial supervision in checking discovery abuse has been modest. Plaintiffs’ main argument against the plausibility standard at the pleading stage is its ostensible conflict with a literal reading of . . . : “a complaint should not be dismissed for failure to state a claim unless it appears beyond doubt that the plaintiff can prove no set of facts in support of his claim which would entitle him to relief.” The “no set of facts” language has been questioned, criticized, and explained away long enough by courts and commentators, and is best forgotten as an incomplete, negative gloss on an accepted pleading standard: once a claim has been stated adequately, it may be supported by showing any set of facts consistent with the allegations in the complaint. [This] described the breadth of opportunity to prove what an adequate complaint claims, not the minimum standard of adequate pleading to govern a complaint’s survival.
Thus, we move to a brave new world of pleading. The application of the old standard, and the intuitive standard that is to a great extent the "living law" were aptly set out in a recent case from the 7th Circuit Court of Appeals:
It is enough to name the plaintiff and the defendant, state the nature of the grievance, and give a few tidbits (such as the date) that will let the defendant investigate. A full narrative is unnecessary. . . .
[T]he belief that complaints must lay out facts corresponding to every “element” of a legal theory [is incorrect]. That is a code-pleading approach, which the Federal Rules of Civil Procedure reject. One pleads “claims” (which is to say, grievances) rather than legal theories and factual specifics. The Supreme Court drove the point home . . . holding that plaintiffs need not allege either the factual or legal “elements” of a prima facie case under the employment-discrimination laws. That conclusion is equally applicable to every other federal claim.
We seem likely to return to an era where a complaint must set forth a factual basis for each element of an alleged civil wrong or breach of contract, something that has long been the better practice, but has not actually been required (although many judges apply the law this way in degradation of the law) for about seventy years.
Even this heightened standard is still far short of the "heightened pleading requirements" that apply in certain kinds of cases, such as those alleging fraud, with a particularly high standard associated with private securities fraud cases.
Never the less, this ruling will have a huge practical impact, simply because it comes up in every single lawsuit ever filed in federal court.