Investments - Realized Gains and Losses on Investments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Investments [Abstract]
Net realized investment gains, excluding credit loss expense and asset write-downs	$ 24	$ 60	$ 33	$ 96
Credit loss (expense) recoveries on invested assets	8	0	(41)	0
Other investment asset write-downs	0	(9)	(10)	(12)
Net realized investment gains (losses), before income taxes	$ 32	$ 51	$ (18)	$ 84