Investments, Aggregate Contractual or Notional Amounts and Estimated Fair Values Related to Derivative Financial Instruments (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
With Hedge Designation [Member] \| Interest Rate Swaps [Member]
Gross Estimated Fair Values of Derivative Positions [Abstract]
Contractual/notional amount	$ 715	$ 715
Liability, estimated fair value	(32)	(8)
Without Hedge Designation [Member] \| Options [Member] \| Purchased [Member]
Gross Estimated Fair Values of Derivative Positions [Abstract]
Contractual/notional amount		57
Asset, estimated fair value		1
Without Hedge Designation [Member] \| Options [Member] \| Written [Member]
Gross Estimated Fair Values of Derivative Positions [Abstract]
Contractual/notional amount		100
Liability, estimated fair value		(1)
Without Hedge Designation [Member] \| Embedded Derivative on Funds Withheld Liability [Member]
Gross Estimated Fair Values of Derivative Positions [Abstract]
Contractual/notional amount	196	182
Liability, estimated fair value	$ (1)	$ (7)

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.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4D
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=118948506&loc=SL51823488-111719

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (a),(c)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624163-113959

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226000-175313

Name:	us-gaap_DerivativeFairValueOfDerivativeLiability
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant