Investment Information - Investment in operating affiliates (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Schedule of Equity Method Investments [Line Items]
Investment in operating affiliates	$ 1,236		$ 1,236		$ 1,119
Income (loss) from operating affiliates	$ 36	$ 54	$ 136	$ 115
Coface
Schedule of Equity Method Investments [Line Items]
Percentage ownership	29.90%		29.90%
Investment in operating affiliates	$ 596		$ 596		570
Greysbridge Holdings Ltd
Schedule of Equity Method Investments [Line Items]
Percentage ownership	40.00%		40.00%
Investment in operating affiliates	$ 521		$ 521		$ 430
Issued Shares Excluding Treasury Stock | Coface
Schedule of Equity Method Investments [Line Items]
Percentage ownership	30.00%		30.00%