Investments - Equity securities reported at fair value (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Debt and Equity Securities, FV-NI [Line Items]
Equity securities	$ 1,559	$ 1,937
Common stocks
Debt and Equity Securities, FV-NI [Line Items]
Equity securities, at cost	1,315	1,164
Equity securities	919	1,283
Equity securities, fair value in excess of cost	(396)	119
Perpetual preferred stocks
Debt and Equity Securities, FV-NI [Line Items]
Equity securities, at cost	685	640
Equity securities	640	654
Equity securities, fair value in excess of cost	(45)	14
Equity securities
Debt and Equity Securities, FV-NI [Line Items]
Equity securities, at cost	2,000	1,804
Equity securities	1,559	1,937
Equity securities, fair value in excess of cost	$ (441)	$ 133