Derivatives (Notes)	12 Months Ended
Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivatives	Derivatives On September 20, 2018, the Company entered into the FX Contract for the JLT Transaction, to hedge the risk of appreciation of the GBP-denominated purchase price. The Company will purchase £5.2 billion at a contracted exchange rate. The settlement of the FX Contract is contingent upon the closing of the JLT Transaction. The all in contract exchange rate includes 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 all in contract exchange rate is fixed through March 29, 2019, increases by .00016 through June 28, 2019 and by 0.000145 each day thereafter until the JLT Transaction closes. 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 was determined using the probability distribution approach, comparing the all in forward rate to the foreign exchange rate for possible dates the JLT Transaction is expected to close, discounted to the valuation date and adjusted for the fair value of the deal contingency feature. The fair value will decrease as the GBP depreciates, or increase as the GBP appreciates, relative to the contracted exchange rate. The fair value related to the deal contingency feature will also decrease (and any unrealized loss increase or any unrealized gain decrease) as conditions to the closing are met. An unrealized loss of $325 million related to the change in fair value of the FX contract was recorded in the consolidated statement of income during 2018 primarily related to the depreciation of the GBP from September 2018. The FX Contract does not qualify for hedge accounting treatment under applicable accounting guidance. The Company expects to record fair value gains or losses, which may be significant, through the consolidated statement of income until the closing of the JLT Transaction. 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 contact. 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 will be recorded in the first quarter of 2019 related to the settlement of the Treasury lock derivatives.

Derivatives

On September 20, 2018, the Company entered into the FX Contract for the JLT Transaction, to hedge the risk of appreciation of the GBP-denominated purchase price. The Company will purchase £5.2 billion at a contracted exchange rate. The settlement of the FX Contract is contingent upon the closing of the JLT Transaction. The all in contract exchange rate includes 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 all in contract exchange rate is fixed through March 29, 2019, increases by .00016 through June 28, 2019 and by 0.000145 each day thereafter until the JLT Transaction closes.

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 was determined using the probability distribution approach, comparing the all in forward rate to the foreign exchange rate for possible dates the JLT Transaction is expected to close, discounted to the valuation date and adjusted for the fair value of the deal contingency feature. The fair value will decrease as the GBP depreciates, or increase as the GBP appreciates, relative to the contracted exchange rate. The fair value related to the deal contingency feature will also decrease (and any unrealized loss increase or any unrealized gain decrease) as conditions to the closing are met. An unrealized loss of $325 million related to the change in fair value of the FX contract was recorded in the consolidated statement of income during 2018 primarily related to the depreciation of the GBP from September 2018. The FX Contract does not qualify for hedge accounting treatment under applicable accounting guidance. The Company expects to record fair value gains or losses, which may be significant, through the consolidated statement of income until the closing of the JLT Transaction.

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 contact. 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 will be recorded in the first quarter of 2019 related to the settlement of the Treasury lock derivatives.