Investments - Holding gains (losses) on equity securities still held (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Holding Gains (Losses) on Equity Securities Still Held [Line Items]
Holding gains (losses) on equity securities still held	$ (9)	$ 16	$ 123	$ (176)
Realized gains (losses) on securities
Holding Gains (Losses) on Equity Securities Still Held [Line Items]
Holding gains (losses) on equity securities still held	(16)	17	82	(174)
Investment income
Holding Gains (Losses) on Equity Securities Still Held [Line Items]
Holding gains (losses) on equity securities still held	$ 7	$ (1)	$ 41	$ (2)