Investments - Additional Information (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Debt Securities [Member]
Schedule of Investments [Line Items]
Interest Receivable	$ 343,000,000	$ 334,000,000
Mortgages [Member]
Schedule of Investments [Line Items]
Interest Receivable	$ 14,000,000	$ 14,000,000

Carrying amount as of the balance sheet date of interest earned but not received. Also called accrued interest or accrued interest receivable.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.8)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_InterestReceivable
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant