Investments - Equity securities reported at fair value (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Debt and Equity Securities, FV-NI [Line Items]
Equity securities	$ 965	$ 889
Common stocks
Debt and Equity Securities, FV-NI [Line Items]
Equity securities, at cost	455	516
Equity securities	561	510
Equity securities, fair value in excess of cost	106	(6)
Perpetual preferred stocks
Debt and Equity Securities, FV-NI [Line Items]
Equity securities, at cost	358	369
Equity securities	404	379
Equity securities, fair value in excess of cost	46	10
Equity securities
Debt and Equity Securities, FV-NI [Line Items]
Equity securities, at cost	813	885
Equity securities	965	889
Equity securities, fair value in excess of cost	$ 152	$ 4