Fair value measurements (Assets, Measured At Fair Value Using Significant Unobservable Inputs) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
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	$ 101	$ 88	$ 87	$ 90
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	2	(2)	(1)	(6)
Purchases, Assets	1	4	19	11
Sales, Assets	(4)	(4)	(5)	(9)
Settlements, Assets	0	0	0	0
Balance-End of Period, Assets	100	86	100	86
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	1	(3)	(1)	(6)
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	5	7	3	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	(1)	0	(1)	(1)
Net Realized Gains/ (Losses), Assets	0	0	0	0
Purchases, Assets	12	(2)	16	3
Sales, Assets	0	(2)	0	(2)
Settlements, Assets	(4)	0	(6)	0
Balance-End of Period, Assets	12	3	12	3
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)	1	(1)	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	718	561	692	564
Transfers Into Level 3, Asset	0	21	1	21
Transfers out of Level 3, Assets	(2)	0	(6)	0
Change in Net Unrealized Gains (Losses) included in OCI, Assets	(6)	15	8	11
Net Realized Gains/ (Losses), Assets	(4)	(1)	(4)	(1)
Purchases, Assets	83	62	155	105
Sales, Assets	(31)	(4)	(51)	(35)
Settlements, Assets	(126)	(5)	(163)	(16)
Balance-End of Period, Assets	632	649	632	649
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	(1)	0	(1)	0
Change in Net Unrealized Gains/Losses included in OCI at the Balance Sheet Date, Assets	(10)	15	3	9
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	2,658	2,544	2,622	2,449
Transfers Into Level 3, Asset	4	3	5	3
Transfers out of Level 3, Assets	0	(2)	(3)	(13)
Change in Net Unrealized Gains (Losses) included in OCI, Assets	4	4	10	2
Net Realized Gains/ (Losses), Assets	(5)	(5)	(5)	(3)
Purchases, Assets	326	118	469	323
Sales, Assets	(87)	(10)	(107)	(30)
Settlements, Assets	(191)	(128)	(282)	(207)
Balance-End of Period, Assets	2,709	2,524	2,709	2,524
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	(2)	(6)	(2)	(2)
Change in Net Unrealized Gains/Losses included in OCI at the Balance Sheet Date, Assets	(1)	3	5	(2)
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	7	10	7	11
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	0	0
Purchases, Assets	15	0	15	0
Sales, Assets	0	0	0	0
Settlements, Assets	(2)	0	(2)	(1)
Balance-End of Period, Assets	20	10	20	10
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

Amount of unrealized gain (loss) recognized in other comprehensive income (OCI) from asset measured at fair value on recurring basis using unobservable input (level 3) and still held.

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- Definition

Indicates line item in statement of income or comprehensive income that includes unrealized gain (loss) from asset measured at fair value using unobservable input (level 3) and still held.

+ References

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Amount of unrealized gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3) and still held.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

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-Topic 820
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Amount of gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3).

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Amount of gain (loss) recognized in other comprehensive income (OCI) from asset measured at fair value on recurring basis using unobservable input (level 3).

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- Definition

Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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- Definition

Amount of sale of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of settlement of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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- Definition

Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy.

+ References

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- Definition

Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy.

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Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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- Definition

Indicates line item in statement of income or comprehensive income that includes gain (loss) from asset measured at fair value using unobservable input (level 3).

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Indicates line item in statement of income or comprehensive income that includes gain (loss) from asset (liability), measured at fair value using unobservable input (level 3).

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