Basis of Presentation

12 Months Ended

Dec. 31, 2012

Basis of Presentation

Basis of Presentation

1.    Basis of Presentation

        The accompanying Consolidated Financial Statements and Notes thereto have been prepared in accordance with U.S. generally accepted accounting principles ("U.S. GAAP"). The Consolidated Financial Statements include the accounts of Aon plc and all controlled subsidiaries ("Aon" or the "Company"). All material intercompany accounts and transactions have been eliminated. The Consolidated Financial Statements as of December 31, 2012 and 2011, and for the years ended December 31, 2012, 2011, and 2010, include, in the opinion of management, all adjustments (consisting of normal recurring adjustments and reclassifications) necessary to present fairly the Company's consolidated financial position, results of operations and cash flows for all periods presented.

Company Redomestication

        On April 2, 2012, the Company completed the reorganization of the corporate structure of the group of companies controlled by its predecessor, Aon Corporation, as holding company of the Aon group, pursuant to which Aon Corporation merged with one of its indirect, wholly-owned subsidiaries and Aon plc became the publicly-held parent company of the Aon group. This transaction is referred to as the Redomestication. In the Redomestication, each issued and outstanding share of Aon Corporation common stock held by stockholders of Aon Corporation was converted into the right to receive one Class A Ordinary Share, nominal value $0.01 per share, of Aon plc. Likewise, equity incentive and compensation plans were assumed by Aon plc and amended to provide that those plans will now provide for the award and issuance of Class A Ordinary Shares instead of shares of common stock of Aon Corporation on a one-for-one basis. Shares of treasury stock of Aon Corporation were cancelled in the Redomestication. Any references to "Aon", "the Company", "us", or "we," or any similar references relating to periods before the Redomestication shall be construed as references to Aon Corporation, being the previous parent company of the Aon group.

Reclassification

        Certain amounts in prior year's consolidated financial statements and related notes have been reclassified to conform to the 2012 presentation. In prior periods, remeasurement gains and losses from foreign currency transactions and related derivative instruments were recognized in Other general expenses in the Consolidated Statements of Income. These gains and losses are now included in Other income (expense) in the Consolidated Statements of Income and disclosed in Note 3 to these Consolidated Financial Statements. The Company believes this provides greater clarity into the income generated from operations.

Use of Estimates

        The preparation of the accompanying Consolidated Financial Statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosures of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenues and expenses. Management evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors, including the current economic environment, which management believes to be reasonable under the circumstances. Aon adjusts such estimates and assumptions when facts and circumstances dictate. Illiquid credit markets, volatile equity markets, and foreign currency movements have combined to increase the uncertainty inherent in such estimates and assumptions. As future events and their effects cannot be determined with precision, actual results could differ significantly from these estimates. Changes in estimates resulting from continuing changes in the economic environment will be reflected in the financial statements in future periods.