Derivatives	3 Months Ended
Mar. 31, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivatives	Derivatives On September 20, 2018, the Company entered into the FX Contract to purchase £5.2 billion at a contracted exchange rate, to hedge the risk of appreciation of the GBP-denominated purchase price of JLT. The settlement of the FX Contract was contingent upon the closing of the JLT Transaction. The all in contract exchange rate included the cost of a liquidity premium (due to the size of the JLT Transaction) and a deal contingent feature, which together increased the exchange rate in the FX Contract to purchase the £5.2 billion by .0343. The FX Contract is measured at fair value and the resulting gain or loss is recorded in the consolidated statements of income. The fair value at March 31, 2019 was based on the all in forward rate, adjusted to exclude the liquidity premium compared to the foreign exchange rate at valuation date. Since all conditions to close had been satisfied at March 31, 2019, no value was assigned to the deal contingency feature. The fair value at December 31, 2018 was determined using the probability distribution approach, comparing the all in forward rate to the foreign exchange rate for possible dates the JLT Transaction could close, discounted to the valuation date and adjusted for the fair value of the deal contingency feature. Determining the fair value of the FX Contract required significant management judgments or estimates about the potential closing dates of the transaction and remaining value of the deal contingency feature. An unrealized gain of $42 million related to the change in fair value during the period from December 31, 2018 to March 31, 2019 was recorded in the consolidated statement of income. This gain resulted from the strengthening of the pound sterling partly offset by the cost of the deal contingency feature. The FX Contract does not qualify for hedge accounting treatment under applicable accounting guidance. The FX Contract was settled on April 1, 2019. A loss of $12 million will be recorded in the second quarter of 2019 related to the settlement of the FX contract. In connection with the JLT Transaction, to hedge the economic risk of changes in future interest rates prior to its issuance of fixed rate debt, in the fourth quarter of 2018 the Company entered into treasury locks related to $2 billion of expected issuances of senior notes in 2019. The fair value at December 31, 2018 is based on the published treasury rate plus forward premium as of December 31, 2018 compared to the all in rate at the inception of the contract. The contracts were not designated as an accounting hedge. The Company recorded an unrealized loss of $116 million related to the change in the fair value of this derivative in the consolidated statement of income for the twelve months ended December 31, 2018. In January 2019, upon issuance of the $5 billion of senior notes, the Company settled the treasury lock derivatives and made a payment to its counter party for $122 million. An additional charge of $6 million was recorded in the first quarter of 2019 related to the settlement of the Treasury lock derivatives. In March 2019, the Company issued €1.1 billion of senior notes related to the JLT Transaction. See Note 14 for additional information related to the Euro senior note issuances. In connection with the senior note issuances, the Company entered into a forward exchange contract to hedge the economic risk of changes in foreign exchange rates from the issuance date to settlement date of the Euro senior notes. This forward exchange contract was settled in March 2019 and the Company recorded a charge of $7.3 million related to the settlement of this contract. Net Investment Hedge The Company has investments in various subsidiaries with Euro functional currencies. As a result, the Company is exposed to the risk of fluctuations between the Euro and U.S. dollar exchange rates. As part of its risk management program to help fund the JLT acquisition, the Company designated the €1.1 billion senior note debt instruments as a net investment hedge of its Euro denominated subsidiaries. The hedge will be re-assessed each quarter to confirm that the designated equity balance at the beginning of each period continues to equal or exceed 80% of the outstanding balance of the Euro debt instrument and that all the critical terms of the hedging instrument and the hedged net investment continue to match. If the Company concludes that the hedge is highly effective, the change in the debt balance related to foreign exchange fluctuations will be recorded in accumulated other comprehensive income (loss) in the consolidated balance sheet. The Company concluded that the hedge was highly effective for the quarter ended March 31, 2019.

Derivatives

On September 20, 2018, the Company entered into the FX Contract to purchase £5.2 billion at a contracted exchange rate, to hedge the risk of appreciation of the GBP-denominated purchase price of JLT. The settlement of the FX Contract was contingent upon the closing of the JLT Transaction. The all in contract exchange rate included the cost of a liquidity premium (due to the size of the JLT Transaction) and a deal contingent feature, which together increased the exchange rate in the FX Contract to purchase the £5.2 billion by .0343.

The FX Contract is measured at fair value and the resulting gain or loss is recorded in the consolidated statements of income. The fair value at March 31, 2019 was based on the all in forward rate, adjusted to exclude the liquidity premium compared to the foreign exchange rate at valuation date. Since all conditions to close had been satisfied at March 31, 2019, no value was assigned to the deal contingency feature. The fair value at December 31, 2018 was determined using the probability distribution approach, comparing the all in forward rate to the foreign exchange rate for possible dates the JLT Transaction could close, discounted to the valuation date and adjusted for the fair value of the deal contingency feature. Determining the fair value of the FX Contract required significant management judgments or estimates about the potential closing dates of the transaction and remaining value of the deal contingency feature. An unrealized gain of $42 million related to the change in fair value during the period from December 31, 2018 to March 31, 2019 was recorded in the consolidated statement of income. This gain resulted from the strengthening of the pound sterling partly offset by the cost of the deal contingency feature. The FX Contract does not qualify for hedge accounting treatment under applicable accounting guidance. The FX Contract was settled on April 1, 2019. A loss of $12 million will be recorded in the second quarter of 2019 related to the settlement of the FX contract.

In connection with the JLT Transaction, to hedge the economic risk of changes in future interest rates prior to its issuance of fixed rate debt, in the fourth quarter of 2018 the Company entered into treasury locks related to $2 billion of expected issuances of senior notes in 2019. The fair value at December 31, 2018 is based on the published treasury rate plus forward premium as of December 31, 2018 compared to the all in rate at the inception of the contract. The contracts were not designated as an accounting hedge. The Company recorded an unrealized loss of $116 million related to the change in the fair value of this derivative in the consolidated statement of income for the twelve months ended December 31, 2018. In January 2019, upon issuance of the $5 billion of senior notes, the Company settled the treasury lock derivatives and made a payment to its counter party for $122 million. An additional charge of $6 million was recorded in the first quarter of 2019 related to the settlement of the Treasury lock derivatives.

In March 2019, the Company issued €1.1 billion of senior notes related to the JLT Transaction. See Note 14 for additional information related to the Euro senior note issuances. In connection with the senior note issuances, the Company entered into a forward exchange contract to hedge the economic risk of changes in foreign exchange rates from the issuance date to settlement date of the Euro senior notes. This forward exchange contract was settled in March 2019 and the Company recorded a charge of $7.3 million related to the settlement of this contract.

Net Investment Hedge

The Company has investments in various subsidiaries with Euro functional currencies. As a result, the Company is exposed to the risk of fluctuations between the Euro and U.S. dollar exchange rates. As part of its risk management program to help fund the JLT acquisition, the Company designated the €1.1 billion senior note debt instruments as a net investment hedge of its Euro denominated subsidiaries. The hedge will be re-assessed each quarter to confirm that the designated equity balance at the beginning of each period continues to equal or exceed 80% of the outstanding balance of the Euro debt instrument and that all the critical terms of the hedging instrument and the hedged net investment continue to match. If the Company concludes that the hedge is highly effective, the change in the debt balance related to foreign exchange fluctuations will be recorded in accumulated other comprehensive income (loss) in the consolidated balance sheet. The Company concluded that the hedge was highly effective for the quarter ended March 31, 2019.