Nature of Operations	6 Months Ended
Jun. 30, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Nature of Operations	Note 1 — Nature of Operations Willis Towers Watson plc is a leading global advisory, broking and solutions company that helps clients around the world turn risk into a path for growth. The Company has more than 45,000 employees and services clients in more than 140 countries. We design and deliver solutions that manage risk, optimize benefits, cultivate talent, and expand the power of capital to protect and strengthen institutions and individuals. Our risk management services include strategic risk consulting (including providing actuarial analysis), a variety of due diligence services, the provision of practical on-site risk control services (such as health and safety and property loss control consulting), and analytical and advisory services (such as hazard modeling and reinsurance optimization studies). We also assist our clients with planning for addressing incidents or crises when they occur. These services include contingency planning, security audits and product tampering plans. We help our clients enhance business performance by delivering consulting services, technology and solutions that optimize benefits and cultivate talent. Our services and solutions encompass such areas as employee benefits, total rewards, talent and benefits outsourcing. In addition, we provide investment advice to help our clients develop disciplined and efficient strategies to meet their investment goals and expand the power of capital. As an insurance broker, we act as an intermediary between our clients and insurance carriers by advising on their risk management requirements, helping them to determine the best means of managing risk and negotiating and placing insurance with insurance carriers through our global distribution network. We operate a private Medicare marketplace in the U.S. through which, along with our active employee marketplace, we help our clients move to a more sustainable economic model by capping and controlling the costs associated with healthcare benefits. Additionally, with the acquisition of TRANZACT in July 2019 (see Note 3 – Acquisitions and Divestitures), we also provide direct-to-consumer sales of Medicare coverage. We are not an insurance company, and therefore we do not underwrite insurable risks for our own account. We believe our broad perspective allows us to see the critical intersections between talent, assets and ideas - the dynamic formula that drives business performance. Proposed Combination with Aon plc On March 9, 2020, WTW and Aon plc (‘Aon’) issued an announcement disclosing that the respective boards of directors of WTW and Aon had reached agreement on the terms of a recommended acquisition of WTW by Aon. Under the terms of the agreement each WTW shareholder will receive 1.08 Aon ordinary shares for each WTW ordinary share. At the time of the announcement, it was estimated that upon completion of the combination, existing Aon shareholders will own approximately 63% and existing WTW shareholders will own approximately 37% of the combined company on a fully diluted basis. The transaction is subject to the approval of the shareholders of both WTW and Aon, as well as other customary closing conditions, including required regulatory approvals. Meetings of the respective shareholders will be held on August 26, 2020. We are required to be in substantial compliance with the Request for Additional Information and Documentary Materials issued by the Antitrust Division of the U.S. Department of Justice on June 29, 2020, referred to as a Second Request. In addition, there are numerous other regulatory approvals and other closing conditions that need to be met. The parties expect the transaction to close in the first half of 2021, subject to satisfaction of these conditions.

Nature of Operations

6 Months Ended

Jun. 30, 2020

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Note 1 — Nature of Operations

Willis Towers Watson plc is a leading global advisory, broking and solutions company that helps clients around the world turn risk into a path for growth. The Company has more than 45,000 employees and services clients in more than 140 countries.

We design and deliver solutions that manage risk, optimize benefits, cultivate talent, and expand the power of capital to protect and strengthen institutions and individuals.

Our risk management services include strategic risk consulting (including providing actuarial analysis), a variety of due diligence services, the provision of practical on-site risk control services (such as health and safety and property loss control consulting), and analytical and advisory services (such as hazard modeling and reinsurance optimization studies). We also assist our clients with planning for addressing incidents or crises when they occur. These services include contingency planning, security audits and product tampering plans.

We help our clients enhance business performance by delivering consulting services, technology and solutions that optimize benefits and cultivate talent. Our services and solutions encompass such areas as employee benefits, total rewards, talent and benefits outsourcing. In addition, we provide investment advice to help our clients develop disciplined and efficient strategies to meet their investment goals and expand the power of capital.

As an insurance broker, we act as an intermediary between our clients and insurance carriers by advising on their risk management requirements, helping them to determine the best means of managing risk and negotiating and placing insurance with insurance carriers through our global distribution network.

We operate a private Medicare marketplace in the U.S. through which, along with our active employee marketplace, we help our clients move to a more sustainable economic model by capping and controlling the costs associated with healthcare benefits. Additionally, with the acquisition of TRANZACT in July 2019 (see Note 3 – Acquisitions and Divestitures), we also provide direct-to-consumer sales of Medicare coverage.

We are not an insurance company, and therefore we do not underwrite insurable risks for our own account. We believe our broad perspective allows us to see the critical intersections between talent, assets and ideas - the dynamic formula that drives business performance.

Proposed Combination with Aon plc

On March 9, 2020, WTW and Aon plc (‘Aon’) issued an announcement disclosing that the respective boards of directors of WTW and Aon had reached agreement on the terms of a recommended acquisition of WTW by Aon. Under the terms of the agreement each WTW shareholder will receive 1.08 Aon ordinary shares for each WTW ordinary share. At the time of the announcement, it was estimated that upon completion of the combination, existing Aon shareholders will own approximately 63% and existing WTW shareholders will own approximately 37% of the combined company on a fully diluted basis.

The transaction is subject to the approval of the shareholders of both WTW and Aon, as well as other customary closing conditions, including required regulatory approvals. Meetings of the respective shareholders will be held on August 26, 2020. We are required to be in substantial compliance with the Request for Additional Information and Documentary Materials issued by the Antitrust Division of the U.S. Department of Justice on June 29, 2020, referred to as a Second Request. In addition, there are numerous other regulatory approvals and other closing conditions that need to be met. The parties expect the transaction to close in the first half of 2021, subject to satisfaction of these conditions.