Investments - Gross realized gains and losses on available for sale fixed maturity investment transactions (Details) - Fixed maturities - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2021	Jun. 30, 2020
Gross realized gains and losses on the sale of available for sale fixed maturity and equity security investments
Gross gains	$ 3	$ 5
Gross losses	$ (1)	$ (3)

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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27357-111563

Name:	us-gaap_DebtSecuritiesAvailableForSaleRealizedGain
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration