Investments (Gains and Losses Recognized on Equity Securities) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Schedule of losses and gains related to equity securities [Line Items]
Net realized gains (losses) on financial instruments	$ 247	$ 1	$ 241	$ 90
Equity Securities [Member]
Schedule of losses and gains related to equity securities [Line Items]
Net realized gains (losses) on financial instruments	188	(16)	183	75
Net realized (losses) gains recognized on sale of equity securities during the period	15	6	20	55
Unrealized (losses) gains recognized on equity securities still held	$ 173	$ (22)	$ 163	$ 20