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Business Combination, Contingent Consideration, Asset, Fair Value Disclosure

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Decrease in Fair Value of Contingent Consideration Due to 5% Decrease in Projections

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Equity Method Investment, Shares Owned

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Increase in Fair Value of Contingent Consideration Due to 5% Increase in Projections

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Amount of realized gain (loss) on investment in debt and equity securities.

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Carrying amount as of the balance sheet date of the asset arising from derivative instruments and hedging activities, which are expected to be converted into cash or otherwise disposed of within a year or the normal operating cycle, if longer.

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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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This item represents the aggregate value of each identified investment accounted for under the equity method of accounting based on the quoted market price for those investments in common stock for which a quoted market price is available.

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This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of gain (loss) recognized on the income statement for financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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This item represents the entity's proportionate share for the period of the net income (loss) of its investee (such as unconsolidated subsidiaries and joint ventures) to which the equity method of accounting is applied. This item includes income or expense related to stock-based compensation based on the investor's grant of stock to employees of an equity method investee.

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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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Amount of investments classified as other.

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The amount of other than temporary impairment (OTTI) losses on equity securities, OTTI related to credit losses on debt securities, and OTTI losses on debt securities when the entity intends to sell the securities or it is more likely than not that the entity will be required to sell the securities before recovery of its amortized cost basis. Additionally, this item includes OTTI losses recognized during the period on investments accounted for under the cost method of accounting.

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Amount of cash inflow from the sale of investments classified as other.

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Price of a single share of a number of saleable stocks of a company.

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Fair Value Measurements (Narrative) (Details) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended		3 Months Ended				6 Months Ended
	Apr. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Jun. 30, 2019 USD ($) $ / shares shares	Mar. 31, 2019 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) $ / shares shares	Jun. 30, 2018 USD ($)	Jun. 30, 2019 R / shares	Dec. 31, 2018 USD ($)	Dec. 31, 2014 R / shares
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net charge for adjustments related to acquisition related accounts							$ 20	$ 11
Increase in fair value of contingent consideration due to 5% increase in projections							45
Decrease in fair value of contingent consideration due to 5% decrease in projections							36
Carrying value of investment			$ 439				439			$ 287
Equity method income			5			$ 2	7	9
Gains on equity investments			3			$ 26	6	$ 19
Other investments			43				$ 43			75
Minimum
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Revenue target period (in years)							2 years
Maximum
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Revenue target period (in years)							4 years
Private Insurance and Consulting
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying value of investment			219				$ 219			61
Private Equity Funds, Non-US
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying value of investment			79				79			82
Equity Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, fair value			$ 18				$ 18			146
Alexander Forbes Group Holdings Limited
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Share price (per share amount) \| R / shares									R 5.79		R 7.50
Percentage of ownership in equity investment			33.00%				33.00%
Carrying value of investment			$ 140				$ 140
Other than temporary impairment					$ 83
Shares owned in investment (in shares) \| shares			443				443
Equity method investment, quoted market value			$ 179				$ 179
Benefitfocus
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from sale of other investments	$ 17	$ 132		$ 115
Payscale
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from sale of other investments			$ 47
Treasury Lock \| Jardine Lloyd Thompson Group plc
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative hedges, assets										2,000
Money Market Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Share price (per share amount) \| $ / shares			$ 1.00				$ 1.00
Fair Value, Measurements, Recurring \| Other Assets
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Contingent purchase consideration asset			$ 65				$ 65			0
Fair Value, Measurements, Recurring \| Other Assets \| Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Contingent purchase consideration asset			$ 65				$ 65			$ 0