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Investment Information - Investment in operating affiliates (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024
Schedule of Equity Method Investments [Line Items]
Investment in operating affiliates	$ 1,305		$ 1,240
Income (loss) from operating affiliates	$ 17	$ 55
Coface
Schedule of Equity Method Investments [Line Items]
Percentage ownership	29.90%
Investment in operating affiliates	$ 650		592
Greysbridge Holdings Ltd
Schedule of Equity Method Investments [Line Items]
Percentage ownership	40.00%
Investment in operating affiliates	$ 538		$ 523
Issued Shares Excluding Treasury Stock | Coface
Schedule of Equity Method Investments [Line Items]
Percentage ownership	30.00%

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