Investments - Equity securities reported at fair value (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Debt and Equity Securities, FV-NI [Line Items]
Equity securities	$ 1,040	$ 1,018
Common stocks
Debt and Equity Securities, FV-NI [Line Items]
Equity securities, at cost	531	512
Equity securities	629	586
Equity securities, fair value in excess of cost	98	74
Perpetual preferred stocks
Debt and Equity Securities, FV-NI [Line Items]
Equity securities, at cost	385	422
Equity securities	411	432
Equity securities, fair value in excess of cost	26	10
Equity securities
Debt and Equity Securities, FV-NI [Line Items]
Equity securities, at cost	916	934
Equity securities	1,040	1,018
Equity securities, fair value in excess of cost	$ 124	$ 84