Investments - Holding gains (losses) on equity securities still held (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Holding Gains (Losses) on Equity Securities Still Held [Line Items]
Holding gains (losses) on equity securities	$ 30	$ (1)	$ 70	$ 5
Realized gains (losses) on securities
Holding Gains (Losses) on Equity Securities Still Held [Line Items]
Holding gains (losses) on equity securities	10	(8)	25	(31)
Net investment income
Holding Gains (Losses) on Equity Securities Still Held [Line Items]
Holding gains (losses) on equity securities	$ 20	$ 7	$ 45	$ 36

Amount of unrealized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(3)(d)(2))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477250/944-220-S99-1

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 321
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479536/321-10-50-4

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