Investments - Investments - Other Than Temporary Impairment (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Credit impairments	$ 1	$ 1	$ 3	$ 1
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net	1	1	3	1
Other than Temporary Impairment Losses, Investments	1	1	3	1
Cumulative Credit Impairments
Beginning balance	(18)	(20)	(19)	(25)
Additions for credit impairments recognized on:
Securities not previously impaired	(1)	0	(3)	0
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, Additional Credit Losses	0	1	0	1
Reductions for credit impairments previously recognized on:
Securities that matured or were sold during the period	0	1	3	6
Ending balance	$ (19)	$ (20)	$ (19)	$ (20)