Fair value measurements (Assets, Measured At Fair Value Using Significant Unobservable Inputs) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Comprehensive Income (Loss), before Tax	Other Comprehensive Income (Loss), before Tax	Other Comprehensive Income (Loss), before Tax	Other Comprehensive Income (Loss), before Tax
Fair Value, Asset (Liability), Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Revenues		Revenues	Revenues
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]		Revenues	Revenues	Revenues
Level 3 | Equity Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance- Beginning of Period, Assets	$ 88	$ 82	$ 90	$ 77
Transfers Into Level 3, Asset	0	0	0	1
Transfers out of Level 3, Assets	0	0	0	0
Change in Net Unrealized Gains (Losses) included in OCI, Assets	0	0	0	0
Net Realized Gains/ (Losses), Assets	(2)		(6)	4
Purchases, Assets	4	0	11	3
Sales, Assets	(4)	(1)	(9)	(4)
Settlements, Assets	0	0	0	0
Balance-End of Period, Assets	86	81	86	81
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	(3)	(1)	(6)	3
Change in Net Unrealized Gains/Losses included in OCI at the Balance Sheet Date, Assets	0	0	0	0
Level 3 | Short-term Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance- Beginning of Period, Assets	7	4	3	7
Transfers Into Level 3, Asset	0	0	0	0
Transfers out of Level 3, Assets	0	0	0	0
Change in Net Unrealized Gains (Losses) included in OCI, Assets	0	0	(1)	0
Net Realized Gains/ (Losses), Assets	0		0	0
Purchases, Assets	(2)	5	3	7
Sales, Assets	(2)	0	(2)	0
Settlements, Assets	0	0	0	(5)
Balance-End of Period, Assets	3	9	3	9
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	0	0	0	0
Change in Net Unrealized Gains/Losses included in OCI at the Balance Sheet Date, Assets	1	0	0	0
Level 3 | Available-for-Sale Debt Securities | Non-U.S.
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance- Beginning of Period, Assets	561	618	564	633
Transfers Into Level 3, Asset	21	5	21	23
Transfers out of Level 3, Assets	0	0	0	(23)
Change in Net Unrealized Gains (Losses) included in OCI, Assets	15	(41)	11	(54)
Net Realized Gains/ (Losses), Assets	(1)		(1)	(2)
Purchases, Assets	62	26	105	69
Sales, Assets	(4)	(19)	(35)	(25)
Settlements, Assets	(5)	(40)	(16)	(72)
Balance-End of Period, Assets	649	549	649	549
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	0	0	0	(2)
Change in Net Unrealized Gains/Losses included in OCI at the Balance Sheet Date, Assets	15	(41)	9	(54)
Level 3 | Available-for-Sale Debt Securities | Corporate and asset-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance- Beginning of Period, Assets	2,544	2,229	2,449	2,049
Transfers Into Level 3, Asset	3	10	3	39
Transfers out of Level 3, Assets	(2)	(43)	(13)	(93)
Change in Net Unrealized Gains (Losses) included in OCI, Assets	4	(30)	2	(52)
Net Realized Gains/ (Losses), Assets	(5)		(3)	0
Purchases, Assets	118	179	323	494
Sales, Assets	(10)	(24)	(30)	(51)
Settlements, Assets	(128)	(60)	(207)	(125)
Balance-End of Period, Assets	2,524	2,261	2,524	2,261
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	(6)	(1)	(2)	(1)
Change in Net Unrealized Gains/Losses included in OCI at the Balance Sheet Date, Assets	3	(30)	(2)	(52)
Level 3 | Available-for-Sale Debt Securities | Mortgage-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance- Beginning of Period, Assets	10	20	11	26
Transfers Into Level 3, Asset	0	0	0	0
Transfers out of Level 3, Assets	0		0	(5)
Change in Net Unrealized Gains (Losses) included in OCI, Assets	0	0	0	0
Net Realized Gains/ (Losses), Assets	0		0	0
Purchases, Assets	0	0	0	0
Sales, Assets	0	0	0	0
Settlements, Assets	0	(1)	(1)	(2)
Balance-End of Period, Assets	10	19	10	19
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	0	0	0	0
Change in Net Unrealized Gains/Losses included in OCI at the Balance Sheet Date, Assets	$ 0	$ 0	$ 0	$ 0