Investments - Allowance for credit losses (Details) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2023 USD ($) securities	Mar. 31, 2023 USD ($)	Jun. 30, 2022 USD ($) securities	Jun. 30, 2023 USD ($) securities	Jun. 30, 2022 USD ($) securities
Allowance for Loan and Lease Losses [Roll Forward]
Balance as of January 1, 2023		$ 7		$ 7	$ 48
Credit losses on securities for which credit losses were not previously recorded		(6)		(7)
Financing Receivable, Allowance for Credit Loss, Sale		49		(2)
Increase (decrease) on securities with allowance recorded in previous period		2
Other-than-temporary Impairment Loss, Debt Securities, Available-for-Sale, Recognized in Earnings	$ 6		$ 2	$ 6	$ 7
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Number of Securities | securities	35		17	37	25
Residential mortgage-backed
Allowance for Loan and Lease Losses [Roll Forward]
Balance as of January 1, 2023		0		$ 0	$ 1
Credit losses on securities for which credit losses were not previously recorded		0
Financing Receivable, Allowance for Credit Loss, Sale		0
Increase (decrease) on securities with allowance recorded in previous period		(1)
Other-than-temporary Impairment Loss, Debt Securities, Available-for-Sale, Recognized in Earnings	$ 2		$ 2	$ 2	$ 7
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Number of Securities | securities	32		17	34	25
Commercial mortgage-backed
Allowance for Loan and Lease Losses [Roll Forward]
Balance as of January 1, 2023		0		$ 0
Credit losses on securities for which credit losses were not previously recorded				(7)
Reductions for securities sold during the period				0
Other-than-temporary Impairment Loss, Debt Securities, Available-for-Sale, Recognized in Earnings	$ 4		$ 0	$ 4	$ 0
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Number of Securities | securities	3		0	3	0
Foreign corporate private securities
Allowance for Loan and Lease Losses [Roll Forward]
Balance as of January 1, 2023		1		$ 1	$ 47
Credit losses on securities for which credit losses were not previously recorded		0		0
Financing Receivable, Allowance for Credit Loss, Sale		49		0
Increase (decrease) on securities with allowance recorded in previous period		3
Foreign corporate public securities and foreign governments
Allowance for Loan and Lease Losses [Roll Forward]
Balance as of January 1, 2023		6		6	$ 0
Credit losses on securities for which credit losses were not previously recorded		(6)		(1)
Financing Receivable, Allowance for Credit Loss, Sale		0		(2)
Increase (decrease) on securities with allowance recorded in previous period		0
U.S. corporate public securities
Allowance for Loan and Lease Losses [Roll Forward]
Balance as of January 1, 2023		$ 0		0
Credit losses on securities for which credit losses were not previously recorded				(1)
Reductions for securities sold during the period				$ 0