Investments - Realized Gains and Losses on Investments (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Investments [Abstract]
Net realized investment (losses) gains, excluding credit loss expense and asset write-downs	$ (24)	$ 11
Credit loss expense on invested assets	(55)	0
Other investment asset write-downs	(9)	(1)
Net realized investment (losses) gains, before income taxes	$ (88)	$ 10