Investments - Equity securities reported at fair value (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Debt and Equity Securities, FV-NI [Line Items]
Equity securities	$ 993	$ 889
Common stocks
Debt and Equity Securities, FV-NI [Line Items]
Equity securities, at cost	464	516
Equity securities	563	510
Equity securities, fair value in excess of cost	99	(6)
Perpetual preferred stocks
Debt and Equity Securities, FV-NI [Line Items]
Equity securities, at cost	386	369
Equity securities	430	379
Equity securities, fair value in excess of cost	44	10
Equity securities
Debt and Equity Securities, FV-NI [Line Items]
Equity securities, at cost	850	885
Equity securities	993	889
Equity securities, fair value in excess of cost	$ 143	$ 4