Investments - Equity securities reported at fair value (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Debt and Equity Securities, FV-NI [Line Items]
Equity securities	$ 1,663	$ 1,937
Common stocks
Debt and Equity Securities, FV-NI [Line Items]
Equity securities, at cost	939	1,164
Equity securities	922	1,283
Equity securities, fair value in excess of cost	(17)	119
Perpetual preferred stocks
Debt and Equity Securities, FV-NI [Line Items]
Equity securities, at cost	702	640
Equity securities	741	654
Equity securities, fair value in excess of cost	39	14
Equity securities
Debt and Equity Securities, FV-NI [Line Items]
Equity securities, at cost	1,641	1,804
Equity securities	1,663	1,937
Equity securities, fair value in excess of cost	$ 22	$ 133