Investments - Investments - Other Than Temporary Impairment (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Credit impairments	$ 0	$ 0	$ 2	$ 0
Intent-to-sell impairments	0	0	0	0
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net	0	0	2	0
Other than Temporary Impairment Losses, Investments	0	0	2	0
Cumulative Credit Impairments
Beginning balance	(18)	(21)	(19)	(25)
Additions for credit impairments recognized on:
Securities not previously impaired	0	0	(2)	0
Reductions for credit impairments previously recognized on:
Securities that matured or were sold during the period	0	1	3	5
Ending balance	$ (18)	$ (20)	$ (18)	$ (20)