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Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings, Net

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

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Amount of increase (decrease) in the value of right to a contingent consideration asset.

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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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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Amount of realized gain (loss) from sale of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Amount of investment in equity security without readily determinable fair value.

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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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No definition available.

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Amount of income (loss) for proportionate share of equity method investee's income (loss).

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- Definition

Balance held at close of period in number of shares.

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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 cash inflow from the sale of investments classified as other.

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The number of shares issued or sold by the subsidiary or equity method investee per stock transaction.

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No definition available.

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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) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended				3 Months Ended				9 Months Ended
	May 31, 2020	Feb. 29, 2020	Apr. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Increase in fair value of contingent consideration due to 5% increase in projections									$ 9
Decrease in fair value of contingent consideration due to 5% decrease in projections									21
Net charge (credit) for adjustments related to acquisition related accounts									8
Carrying value of investment					$ 265				265		$ 434
Equity securities					58				58		19
Gain (loss) on equity securities					(16)	$ 4			(19)	$ 10
Equity investments without readily determinable market value					43				$ 43		67
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					169				$ 169		183
Private Equity Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying value of investment					96				96		$ 107
Equity method income (loss)					2	$ 3			(6)	$ 10
Alexander Forbes Group Holdings Limited
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity method investment, shares owned											443
Number of shares sold (shares)	193	49
Investments, fair value					$ 41				41
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
Unobservable Inputs (Level 3) \| Fair Value, Measurements, Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Change in contingent purchase consideration									14
Increase in fair value of contingent consideration due to 5% increase in projections									6
Decrease in fair value of contingent consideration due to 5% decrease in projections									$ 6
Money Market Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Share price (per share amount)					$ 1.00				$ 1.00
Alexander Forbes Group Holdings Limited
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment owned, shares					201				201