Investments - Holding gains (losses) on equity securities still held (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Holding Gains (Losses) on Equity Securities Still Held [Line Items]
Realized gains (losses) on securities still owned	$ 45	$ (18)	$ (302)	$ 222
Included in net investment income	578	593	1,601	1,727
Equity securities
Holding Gains (Losses) on Equity Securities Still Held [Line Items]
Realized gains (losses) on securities still owned	30	(16)	(303)	210
Equity securities still owned | Equity securities | Accounting Standards Update 2016-01
Holding Gains (Losses) on Equity Securities Still Held [Line Items]
Net holding gains (losses) on equity securities	19	(7)	(299)	180
Equity securities still owned | Realized gains (losses) on securities | Equity securities | Accounting Standards Update 2016-01
Holding Gains (Losses) on Equity Securities Still Held [Line Items]
Realized gains (losses) on securities still owned	23	(24)	(300)	146
Equity securities still owned | Investment income | Equity securities | Accounting Standards Update 2016-01
Holding Gains (Losses) on Equity Securities Still Held [Line Items]
Included in net investment income	$ (4)	$ 17	$ 1	$ 34