Fair value measurements (Assets, Measured At Fair Value Using Significant Unobservable Inputs) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
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 income tax	Other comprehensive income (loss), before income tax	Other comprehensive income (loss), before income tax	Other comprehensive income (loss), before income tax
Fair Value, Asset (Liability), Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Revenues	Revenues	Revenues	Revenues
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Revenues	Revenues	Revenues	Revenues
Level 3 | Equity Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance- Beginning of Period, Assets	$ 113	$ 101	$ 120	$ 87
Transfers Into Level 3, Asset	0	0	0	0
Transfers out of Level 3, Assets	(1)	0	(1)	0
Change in Net Unrealized Gains (Losses) included in OCI, Assets	0	0	0	0
Net Realized Gains/ (Losses), Assets	2	2	(3)	(1)
Purchases, Assets	19	1	26	19
Sales, Assets	(8)	(4)	(17)	(5)
Settlements, Assets	0	0	0	0
Balance-End of Period, Assets	125	100	125	100
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	4	1	9	(1)
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	18	5	14	3
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	(1)	0	(1)
Net Realized Gains/ (Losses), Assets	0	0	0	0
Purchases, Assets	25	12	30	16
Sales, Assets	0	0	0	0
Settlements, Assets	(1)	(4)	(2)	(6)
Balance-End of Period, Assets	42	12	42	12
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	(1)	0	(1)
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	587	718	604	692
Transfers Into Level 3, Asset	10	0	11	1
Transfers out of Level 3, Assets	0	(2)	0	(6)
Change in Net Unrealized Gains (Losses) included in OCI, Assets	18	(6)	38	8
Net Realized Gains/ (Losses), Assets	3	(4)	(3)	(4)
Purchases, Assets	84	83	144	155
Sales, Assets	(34)	(31)	(87)	(51)
Settlements, Assets	(70)	(126)	(109)	(163)
Balance-End of Period, Assets	598	632	598	632
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	0	(1)	(1)	(1)
Change in Net Unrealized Gains/Losses included in OCI at the Balance Sheet Date, Assets	16	(10)	30	3
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	3,017	2,658	2,891	2,622
Transfers Into Level 3, Asset	60	4	84	5
Transfers out of Level 3, Assets	(12)	0	(13)	(3)
Change in Net Unrealized Gains (Losses) included in OCI, Assets	(3)	4	(7)	10
Net Realized Gains/ (Losses), Assets	(4)	(5)	(6)	(5)
Purchases, Assets	295	326	514	469
Sales, Assets	(53)	(87)	(100)	(107)
Settlements, Assets	(114)	(191)	(177)	(282)
Balance-End of Period, Assets	3,186	2,709	3,186	2,709
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	(1)	(2)	(4)	(2)
Change in Net Unrealized Gains/Losses included in OCI at the Balance Sheet Date, Assets	(7)	(1)	(17)	5
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	0	7	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	0	0
Net Realized Gains/ (Losses), Assets	0	0	(2)	0
Purchases, Assets	0	15	1	15
Sales, Assets	0	0	(2)	0
Settlements, Assets	0	(2)	0	(2)
Balance-End of Period, Assets	0	20	0	20
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