Investments - Holding gains (losses) on equity securities still held (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Holding Gains (Losses) on Equity Securities Still Held [Line Items]
Realized gains (losses) on securities	$ 110	$ (75)	$ 155
Investment income	742	467	538
Equity securities
Holding Gains (Losses) on Equity Securities Still Held [Line Items]
Realized gains (losses) on securities	110	(70)	155
Equity securities still owned | Equity securities
Holding Gains (Losses) on Equity Securities Still Held [Line Items]
Net holding gains (losses) on equity securities	119	(32)	126
Realized gains (losses) on securities | Equity securities still owned | Equity securities
Holding Gains (Losses) on Equity Securities Still Held [Line Items]
Realized gains (losses) on securities	65	(44)	105
Investment income | Equity securities still owned | Equity securities
Holding Gains (Losses) on Equity Securities Still Held [Line Items]
Investment income	$ 54	$ 12	$ 21