Fair value measurements (Assets, Measured At Fair Value Using Significant Unobservable Inputs) (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2025	Mar. 31, 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
Fair Value, Asset (Liability), Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Revenues	Revenues
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Revenues	Revenues
Level 3 \| Equity Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance- Beginning of Period, Assets	$ 120	$ 87
Transfers Into Level 3, Asset	0	0
Transfers out of Level 3, Assets	0	0
Change in Net Unrealized Gains (Losses) included in OCI, Assets	0	0
Net Realized Gains/ (Losses), Assets	(5)	(3)
Purchases, Assets	7	18
Sales, Assets	(9)	(1)
Settlements, Assets	0	0
Balance-End of Period, Assets	113	101
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	5	(2)
Change in Net Unrealized Gains/Losses included in OCI at the Balance Sheet Date, Assets	0	0
Level 3 \| Short-term Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance- Beginning of Period, Assets	14	3
Transfers Into Level 3, Asset	0	0
Transfers out of Level 3, Assets	0	0
Change in Net Unrealized Gains (Losses) included in OCI, Assets	0	0
Net Realized Gains/ (Losses), Assets	0	0
Purchases, Assets	5	4
Sales, Assets	0	0
Settlements, Assets	(1)	(2)
Balance-End of Period, Assets	18	5
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	0	0
Change in Net Unrealized Gains/Losses included in OCI at the Balance Sheet Date, Assets	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	604	692
Transfers Into Level 3, Asset	1	1
Transfers out of Level 3, Assets	0	(4)
Change in Net Unrealized Gains (Losses) included in OCI, Assets	20	14
Net Realized Gains/ (Losses), Assets	(6)	0
Purchases, Assets	60	72
Sales, Assets	(53)	(20)
Settlements, Assets	(39)	(37)
Balance-End of Period, Assets	587	718
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	(1)	0
Change in Net Unrealized Gains/Losses included in OCI at the Balance Sheet Date, Assets	14	13
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	2,891	2,622
Transfers Into Level 3, Asset	24	1
Transfers out of Level 3, Assets	(1)	(3)
Change in Net Unrealized Gains (Losses) included in OCI, Assets	(4)	6
Net Realized Gains/ (Losses), Assets	(2)	0
Purchases, Assets	219	143
Sales, Assets	(47)	(20)
Settlements, Assets	(63)	(91)
Balance-End of Period, Assets	3,017	2,658
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	(3)	0
Change in Net Unrealized Gains/Losses included in OCI at the Balance Sheet Date, Assets	(10)	6
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	3	7
Transfers Into Level 3, Asset	0	0
Transfers out of Level 3, Assets	0	0
Change in Net Unrealized Gains (Losses) included in OCI, Assets	0	0
Net Realized Gains/ (Losses), Assets	(2)	0
Purchases, Assets	1	0
Sales, Assets	(2)	0
Settlements, Assets	0	0
Balance-End of Period, Assets	0	7
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	0	0
Change in Net Unrealized Gains/Losses included in OCI at the Balance Sheet Date, Assets	$ 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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
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-Publisher FASB
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- Definition

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.

+ References

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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

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 101
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482078/820-10-55-101

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

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

+ References

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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.

+ References

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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.

+ References

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- Definition

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.

+ References

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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.

+ References

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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).

+ References

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- Definition

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).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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-Name Accounting Standards Codification
-Section 50
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-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

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