Investments - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Investments related to 2012 contract conversion	$ 450	$ 524
Residential mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Weighted average duration of securities	4 years 8 months 12 days
Commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Weighted average duration of securities	6 years 1 month 6 days
Other asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Weighted average duration of securities	1 year

The aggregate value of all restricted investments.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 954
-SubTopic 210
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=120413173&loc=SL6242262-115580

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 320
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-12.6(c))
-URI http://asc.fasb.org/extlink&oid=122147990&loc=d3e611133-123010

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 954
-SubTopic 210
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=120413209&loc=SL6242269-115581

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 320
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-12B(Footnote 11(c)))
-URI http://asc.fasb.org/extlink&oid=122147990&loc=d3e611197-123010

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