Investments - Equity securities reported at fair value (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Debt and Equity Securities, FV-NI [Line Items]
Equity securities	$ 1,606	$ 1,937
Common stocks
Debt and Equity Securities, FV-NI [Line Items]
Equity securities, at cost	1,145	1,164
Equity securities	874	1,283
Equity securities, fair value in excess of cost	(271)	119
Perpetual preferred stocks
Debt and Equity Securities, FV-NI [Line Items]
Equity securities, at cost	724	640
Equity securities	732	654
Equity securities, fair value in excess of cost	8	14
Equity securities
Debt and Equity Securities, FV-NI [Line Items]
Equity securities, at cost	1,869	1,804
Equity securities	1,606	1,937
Equity securities, fair value in excess of cost	$ (263)	$ 133