Investments - Equity securities reported at fair value (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Debt and Equity Securities, FV-NI [Line Items]
Equity securities	$ 1,937	$ 1,814
Common stocks
Debt and Equity Securities, FV-NI [Line Items]
Equity securities, at cost	1,164	1,241
Equity securities	1,283	1,148
Equity securities, fair value in excess of cost	119	(93)
Perpetual preferred stocks
Debt and Equity Securities, FV-NI [Line Items]
Equity securities, at cost	640	705
Equity securities	654	666
Equity securities, fair value in excess of cost	14	(39)
Equity securities
Debt and Equity Securities, FV-NI [Line Items]
Equity securities, at cost	1,804	1,946
Equity securities	1,937	1,814
Equity securities, fair value in excess of cost	$ 133	$ (132)