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

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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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Amount of loss from downward price adjustment on investment in equity security without readily determinable fair value.

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Amount of gain from upward price adjustment on investment in equity security without readily determinable fair value.

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- Definition

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 in income from liability measured at fair value on recurring basis using unobservable input (level 3).

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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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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		12 Months Ended
	May 31, 2020	Feb. 29, 2020	Apr. 30, 2019	Mar. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Increase in fair value of contingent consideration due to 5% increase in projections							$ 12
Net increase in estimated fair value of liabilities related to prior period acquisitions							11	$ 70
Decrease in fair value of contingent consideration due to 5% decrease in projections							21
Equity method investments							280	434
Equity method income								12	$ 17
Gain (loss) on equity securities							(27)	10	$ 54
Other investments							$ 33	$ 67
Alexander Forbes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment owned, balance (in shares)							201
Alexander Forbes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity investment shares owned by the Company (in shares)								443
Sale of stock, number of shares issued in transaction (in shares)	193	49
Investments, fair value							$ 54
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
Private Insurance and Consulting
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity method investments							169	$ 183
Private Equity Investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity method investments							111	107
Equity method income							3	13
Equity Investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, fair value							72	19
Other Investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity securities without readily determinable fair value, upward price adjustment, annual amount							$ 2
Equity securities without readily determinable fair value, downward price adjustment, annual amount								$ 1
Minimum
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Revenue target period							2 years
Maximum
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Revenue target period							4 years
Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Share price (in dollars per share)							$ 1.00