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Investment Information - Investments in operating affiliates (Details) € / shares in Units, $ / shares in Units, € in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($) $ / shares	Dec. 31, 2021 EUR (€) € / shares
Schedule of Equity Method Investments [Line Items]
Investment in operating affiliates	$ 1,240	$ 1,119
Income (loss) from operating affiliates	$ 200	184	$ 75
Coface
Schedule of Equity Method Investments [Line Items]
Percentage ownership	29.90%			29.50%	29.50%
Investment in affiliate, price per share | € / shares					€ 9.95
Equity method investment, aggregate cost				$ 546	€ 453
Operating affiliate gain on acquisition				75
Operating affiliates , deferred gain on acquisition				$ 36
Operating affiliates, deferred gain on acquisition, amortization period				5 years
Investment in operating affiliates	$ 592	570
Coface | Issued Shares Excluding Treasury Stock
Schedule of Equity Method Investments [Line Items]
Percentage ownership	30.03%
Greysbridge Holdings Ltd
Schedule of Equity Method Investments [Line Items]
Percentage ownership				40.00%	40.00%
Investment in affiliate, price per share | $ / shares				$ 35.00
Equity method investment, aggregate cost				$ 279
Operating affiliate gain on acquisition				$ 96
Investment in operating affiliates	$ 523	$ 430
Greysbridge Holdings Ltd | Kelso And Company
Schedule of Equity Method Investments [Line Items]
Percentage ownership				30.00%	30.00%
Greysbridge Holdings Ltd | Warburg Pincus LLC
Schedule of Equity Method Investments [Line Items]
Percentage ownership				30.00%	30.00%

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