Investments - Realized Capital Gains and Losses by Transaction Type (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Investments [Abstract]
Impairment write-downs	$ (8)	$ (4)	$ (20)	$ (7)
Sales	20	(2)	20	(14)
Valuation of equity investments	5	50	203	37
Valuation and settlements of derivative instruments	8	4	16	8
Total realized capital gains and losses	$ 25	$ 48	$ 219	$ 24