Investments - Holding gains (losses) on equity securities still held (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Holding Gains (Losses) on Equity Securities Still Held [Line Items]
Realized gains (losses) on securities still owned	$ 184	$ (93)
Included in net investment income	548	500
Equity securities
Holding Gains (Losses) on Equity Securities Still Held [Line Items]
Realized gains (losses) on securities still owned	182	(95)
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	174	(95)
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	163	(94)
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	$ 11	$ (1)