Investments - Investments - Securities Lending and Repurchase Agreements (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Dec. 31, 2018
Securities Lending Transactions:
Gross amount of securities on loan	$ 675	$ 820
Gross amount of associated liability for collateral received	691	840
Repurchase agreements:
Gross amount of recognized liabilities for repurchase agreements	300	72
Gross amount of collateral pledged related to repurchase agreements	303	73
Securities for Reverse Repurchase Agreements	83	64
Federal Home Loan Bank Borrowings, Fair Value Disclosure	50	0
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged	60	0
Securities Loaned, Collateral, Obligation to Return Securities	1	3
Federal Home Loan Bank Stock	$ 9	$ 10
Minimum
Repurchase agreements:
Securities Sold Under Agreements to Repurchase, Percentage of Fair Value Required to be Paid in Cash at Sale	95.00%
Federal Home Loan Bank, Advances, Maturities Summary, Due in Year Three	40.00%
Maxum [Member]
Repurchase agreements:
Federal Home Loan Bank, Advances, Maturities Summary, Due in Year Three	97.00%

Percentage of the fair value of the assets pledged as collateral

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- Definition

Securities Loaned, Collateral, Obligation to Return

+ References

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- Definition

Securities Loaned, Collateral, Obligation to Return Securities

+ References

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- Definition

Securities Sold Under Agreements to Repurchase, Collateral, Obligation to Return

+ References

No definition available.

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- Definition

Securities Sold Under Agreements to Repurchase, Percentage of Fair Value Required to be Paid in Cash at Sale

+ References

No definition available.

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- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
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- Definition

Fair value portion of borrowing from Federal Home Loan Bank (FHLBank).

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
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- Definition

Federal Home Loan Bank (FHLB) stock represents an equity interest in a FHLB. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-SubTopic 325
-Section 45
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- Definition

The carrying value of securities purchased to be resold in reverse repurchase transactions as of the balance sheet date.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
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- Definition

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

+ References

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-Publisher FASB
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- References

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Amount, before 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 elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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