H and W married in 1973 and have two children. H is a partner at a New York law firm and W, also an attorney, is employed by a university. The parties separated in 2002 and stipulated in 2004 that the cut-off date for determining the value of marital assets would be September 1, 2004. H and W spent two years negotiating a detailed 22-page settlement agreement, executed in June 2006. In August 2006, the settlement agreement was incorporated, but not merged, into the parties' final judgment of divorce. H agreed to pay W $6,250,000 'as and for an equitable distribution of property and in satisfaction of W's support and marital property rights.' W retained title to a Manhattan apartment (subject to a $370,000 mortgage), an automobile, her retirement accounts, and any 'bank, brokerage and similar financial accounts in her name.' Upon receipt of her distributive payment, W agreed to convey her interest in the Scarsdale marital residence to H. H received title to three automobiles and kept his retirement accounts, less $368,000 to equalize the value of the parties' retirement accounts. H further retained 'bank, brokerage and similar financial accounts' that were in his name, two of which were specifically referenced--his capital account as a partner at the law firm and a Citibank account. Although the agreement acknowledged that the property division was 'fair and reasonable,' it did not state that the parties intended an equal distribution or other designated percentage division of the marital estate. The only provision that explicitly contemplated an equal division was the reference to equalizing the values of the parties' retirement accounts. The settlement constituted 'an agreement between them with respect to any and all funds, assets or properties, both real and personal, including property in which either of them may have an equitable or beneficial interest wherever situated, now owned by the parties or either of them, or standing in their respective names or which may hereafter be acquired by either of them, and all other rights and obligations arising out of the marital relationship.' One of H's unspecified brokerage accounts was maintained by Bernard L. Madoff Investment Securities. The parties believed the account was valued at $5.4 million as of September 1, 2004. In December 2008, Madoff's Ponzi scheme was publicly exposed. H commenced this action against W alleging two causes of action: (1) reformation of the settlement agreement predicated on a mutual mistake and (2) unjust enrichment. H now asserts that the settlement agreement was intended to accomplish an 'approximately equal division of marital assets, including a 50-50 division of the Madoff account. To that end, the amended complaint states that $2,700,000 of W's $6,250,000 distributive payment represented her 'share' of the Madoff account. H states that both parties operated under the 'mistake' or misconception as to the existence of a legitimate investment account with Madoff which was revealed to be part of a fraudulent Ponzi scheme. The Supreme Court granted W's motion and dismissed the amended complaint. The Appellate Division, with two Justices dissenting, reversed and reinstated the action. W appealed on a certified question.