Derivatives (Credit Risk on Freestanding Derivatives) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Credit Derivatives [Line Items]
Derivative Liability, Fair Value, Gross Liability	$ 3,223	$ 3,129
Estimated Fair Value of Derivatives in Net Liability Position	1,377	1,138
Accrued Investment Income Receivable	583	575
Premiums and Other Receivables, Net	13,024	12,918
Fixed Maturity Securities
Credit Derivatives [Line Items]
Estimated Fair Value of Collateral Provided	$ 1,690	$ 1,414

Interest, dividends, rents, ancillary and other revenues earned but not yet received by the entity on its investments.

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The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

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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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Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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The aggregate fair value amounts of derivative instruments that contain credit-risk-related contingent features that are in a net liability position at the end of the reporting period. For nonderivative instruments that are designated and qualify as hedging instruments, the fair value amounts are the carrying value of the nonderivative hedging instrument, including the adjustment for the foreign currency transaction gain (loss) on that instrument.

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Carrying amount as of the balance sheet date, net of allowance for doubtful accounts, of all premiums and other types of receivables due from other persons or entities.

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