Does a Rule 12(b)(6) motion to dismiss need detailed factual allegations?

"While a complaint attacked by a Rule 12(b)(6) 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 . . . ." Twombly, 550 U.S. at 555 (citation omitted). "Threadbare recitals of the elements of a cause of action, supported by mere conclusory statements, do not suffice," and "the tenet that a court must accept as true all of the allegations contained in a complaint is inapplicable to legal conclusions." Ashcroft v. Iqbal, 556 U.S. 662, 678 (2009).