Investments - Realized Gains and Losses on Investments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Investments [Abstract]
Net realized investment gains (losses), excluding credit loss expense and asset write-downs	$ 186	$ 189	$ (34)
Credit loss (expense) recoveries on invested assets	(27)	0	0
Other investment asset write-downs	(10)	(12)	(47)
Net realized investment gains (losses), before income taxes	$ 149	$ 177	$ (81)