Commitments, contingencies, and guarantees Commitments, Contingencies, And Guarantees (Transactions accounted for as secured borrowings) (Details) - USD ($) $ in Millions		Dec. 31, 2023	Dec. 31, 2022
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending collateral		$ 1,299	$ 1,523
Collateral held under securities lending agreements		1,299	1,523
Repurchase Agreements [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Secured Borrowings, Gross, Difference, Amount	[1]	91	108
Maturity Overnight [Member] | Cash
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending collateral		555	820
Maturity Overnight [Member] | U.S. Treasury / Agency
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending collateral		33	72
Maturity Overnight [Member] | Foreign [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending collateral		621	604
Maturity Overnight [Member] | Corporate securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending collateral		57	27
Maturity Overnight [Member] | Equity securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending collateral		27	0
Maturity Overnight [Member] | States, municipalities, and political subdivisions
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending collateral		$ 6	$ 0

[1] Per the repurchase agreements, the amount of collateral posted is required to exceed the amount of gross liability.