Investments - Investments - Securities Lending, Repurchase Agreements, and Other Collateral Transactions (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Securities Lending Transactions:
Gross amount of securities on loan	$ 344	$ 606
Gross amount of associated liability for collateral received	352	621
Repurchase agreements:
Securities for Reverse Repurchase Agreements	14	15
Securities Loaned, Collateral, Obligation to Return Securities	0	34
Assets Held by Insurance Regulators	2,500	2,300
Short-term investments	2,505	2,921
Debt Securities [Member]
Repurchase agreements:
Debt Securities, Available-for-sale, Restricted	573	447
Short-term investments
Repurchase agreements:
Short-term investments	50	189
US Treasury Securities [Member]
Repurchase agreements:
Debt Securities, Available-for-sale, Restricted	$ 34	37
Minimum
Repurchase agreements:
Securities Sold Under Agreements to Repurchase, Percentage of Fair Value Required to be Paid in Cash at Sale	95.00%
Fair Value Measured at Net Asset Value Per Share [Member]
Repurchase agreements:
Deposit Assets	$ 40	$ 38

Securities Loaned, Collateral, Obligation to Return

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Securities Loaned, Collateral, Obligation to Return Securities

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

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Carrying amount of cash and investment securities on deposit with state regulatory authorities in connection with capital requirements.

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Amount of restricted investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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The carrying amount of the asset transferred to a third party to serve as a deposit, which typically serves as security against failure by the transferor to perform under terms of an agreement.

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Amount of short-term investments classified as other.

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

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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.

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