Investments - Investments - Other Than Temporary Impairment (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Credit impairments	$ 2	$ 0
Intent-to-sell impairments	0	0
Impairments on equity securities and other impairments	2	0
Other than Temporary Impairment Losses, Investments	2	0
Cumulative Credit Impairments
Beginning balance	(19)	(25)
Additions for credit impairments recognized on:
Securities not previously impaired	(2)	0
Reductions for credit impairments previously recognized on:
Securities that matured or were sold during the period	3	4
Ending balance	$ (18)	$ (21)