Investments (Securities Lending, Repurchase Agreements and FHLB Agreements) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	$ 19,718	$ 17,369
Reinvestment portfolio - estimated fair value	19,541	17,451
Security collateral on deposit from counterparties	21	0
Estimated fair value
Securities Financing Transaction [Line Items]
Securities loaned	19,170	16,926
Repurchase Agreements
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	2,700	2,310
Reinvestment portfolio - estimated fair value	2,676	2,320
Repurchase Agreements \| Estimated fair value
Securities Financing Transaction [Line Items]
Securities Sold under Agreements to Repurchase	2,746	2,333
Federal Home Loan Bank of Boston
Securities Financing Transaction [Line Items]
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Amount of Advances	800	800
Federal Home Loan Bank of Boston \| Estimated fair value
Securities Financing Transaction [Line Items]
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged	1,132	1,083
Fixed Maturity Securities \| Federal Home Loan Bank of Boston
Securities Financing Transaction [Line Items]
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Amount of Advances	$ 807	$ 843

This element represents the estimated fair value of the securities lending reinvestment portfolio.

No definition available.

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- Definition

Amount of advances from the Federal Home Loan Bank (FHLB).

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- Definition

Amount of the collateral pledged in support of federal home loan bank advances outstanding.

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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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- Definition

Amount, after the effects of master netting arrangements, of securities loaned to entities in exchange for collateral. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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- Definition

The carrying value as of the balance sheet date of the assets received as collateral against securities loaned to other broker-dealers. Borrowers of securities generally are required to provide collateral to the lenders of securities, commonly cash but sometimes other securities or standby letters of credit, with a value slightly higher than that of the securities borrowed. In instances where the entity is permitted to sell or re-pledge these securities, the entity reports the fair value of the collateral received and the related obligation to return the collateral as a liability.

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Amount, after the effects of master netting arrangements, of funds outstanding borrowed in the form of a security repurchase agreement between the entity and another party for the sale and repurchase of identical or substantially the same securities at a date certain for a specified price. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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- Definition

Carrying amount of liabilities associated with financial assets accounted for as secured borrowings recognized in the transferor's statement of financial position at the end of each period presented.

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