Investments - Equity securities reported at fair value (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Debt and Equity Securities, FV-NI [Line Items]
Equity securities	$ 944	$ 889
Common stocks
Debt and Equity Securities, FV-NI [Line Items]
Equity securities, at cost	467	516
Equity securities	536	510
Equity securities, fair value in excess of cost	69	(6)
Perpetual preferred stocks
Debt and Equity Securities, FV-NI [Line Items]
Equity securities, at cost	371	369
Equity securities	408	379
Equity securities, fair value in excess of cost	37	10
Equity securities
Debt and Equity Securities, FV-NI [Line Items]
Equity securities, at cost	838	885
Equity securities	944	889
Equity securities, fair value in excess of cost	$ 106	$ 4