Accounting Principles and Practices	6 Months Ended
Jun. 30, 2014
Accounting Policies [Abstract]
Accounting Principles and Practices	Accounting Principles and Practices Changes in Accounting Principles Revenue Recognition In May 2014, the Financial Accounting Standards Board ("FASB") issued new accounting guidance on revenue from contracts with customers, which will supersede nearly all existing revenue recognition guidance under U.S. GAAP. The core principal of the guidance is that an entity should recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The guidance also requires additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts, including significant judgments and changes in judgments and assets recognized from costs incurred to obtain or fulfill a contract. The guidance is effective for Aon in the first quarter of 2017 and early adoption is not permitted. The guidance permits two methods of transition upon adoption; full retrospective and modified retrospective. Under the full retrospective method, prior periods would be restated under the new revenue standard, providing a comparable view across all periods presented. Under the modified retrospective method, prior periods would not be restated. Rather, revenues and other disclosures for pre-2017 periods would be provided in the notes to the financial statements as previously reported under the current revenue standard. The impact from the adoption of this guidance on the Company's Condensed Consolidated Financial Statements cannot be determined at this time. The Company is also working to determine the appropriate method of transition to the guidance. Discontinued Operations In April 2014, the FASB issued new accounting guidance that increased the threshold for a disposal to qualify as a discontinued operation and requires new disclosures of both discontinued operations and certain other disposals that do not meet the definition of a discontinued operation. The guidance is effective for Aon in the first quarter of 2015. The adoption of this guidance is not expected to have a material impact on the Company's Condensed Consolidated Financial Statements. Presentation of Unrecognized Tax Benefits In July 2013, the FASB issued guidance on the presentation of certain unrecognized tax benefits on financial statements. The guidance requires, unless certain conditions exist, an unrecognized tax benefit to be presented as a reduction to a deferred tax asset in the financial statements for a net operating loss carryforward, a similar tax loss, or a tax credit carryforward. The guidance was effective for Aon in the first quarter of 2014. The adoption of this guidance did not have a material impact on the Company's Condensed Consolidated Financial Statements. Foreign Currency In March 2013, the FASB issued new accounting guidance clarifying the accounting for the release of cumulative translation adjustment into net income when a parent either sells a part or all of its investment in a foreign entity or no longer holds a controlling financial interest in a subsidiary or group of assets that is a nonprofit activity or a business within a foreign entity. The guidance was effective for Aon in the first quarter of 2014. The adoption of this guidance did not have a material impact on the Company's Condensed Consolidated Financial Statements.

Accounting Principles and Practices

Changes in Accounting Principles

Revenue Recognition

In May 2014, the Financial Accounting Standards Board ("FASB") issued new accounting guidance on revenue from contracts with customers, which will supersede nearly all existing revenue recognition guidance under U.S. GAAP. The core principal of the guidance is that an entity should recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The guidance also requires additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts, including significant judgments and changes in judgments and assets recognized from costs incurred to obtain or fulfill a contract. The guidance is effective for Aon in the first quarter of 2017 and early adoption is not permitted. The guidance permits two methods of transition upon adoption; full retrospective and modified retrospective. Under the full retrospective method, prior periods would be restated under the new revenue standard, providing a comparable view across all periods presented. Under the modified retrospective method, prior periods would not be restated. Rather, revenues and other disclosures for pre-2017 periods would be provided in the notes to the financial statements as previously reported under the current revenue standard. The impact from the adoption of this guidance on the Company's Condensed Consolidated Financial Statements cannot be determined at this time. The Company is also working to determine the appropriate method of transition to the guidance.

Discontinued Operations

In April 2014, the FASB issued new accounting guidance that increased the threshold for a disposal to qualify as a discontinued operation and requires new disclosures of both discontinued operations and certain other disposals that do not meet the definition of a discontinued operation. The guidance is effective for Aon in the first quarter of 2015. The adoption of this guidance is not expected to have a material impact on the Company's Condensed Consolidated Financial Statements.

Presentation of Unrecognized Tax Benefits

In July 2013, the FASB issued guidance on the presentation of certain unrecognized tax benefits on financial statements. The guidance requires, unless certain conditions exist, an unrecognized tax benefit to be presented as a reduction to a deferred tax asset in the financial statements for a net operating loss carryforward, a similar tax loss, or a tax credit carryforward. The guidance was effective for Aon in the first quarter of 2014. The adoption of this guidance did not have a material impact on the Company's Condensed Consolidated Financial Statements.

Foreign Currency

In March 2013, the FASB issued new accounting guidance clarifying the accounting for the release of cumulative translation adjustment into net income when a parent either sells a part or all of its investment in a foreign entity or no longer holds a controlling financial interest in a subsidiary or group of assets that is a nonprofit activity or a business within a foreign entity. The guidance was effective for Aon in the first quarter of 2014. The adoption of this guidance did not have a material impact on the Company's Condensed Consolidated Financial Statements.