Investments (OTTI rollforward) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
OTTI Credit Losses Recognized in Earnings Rollforward
Beginning balance	$ 2	$ 2	$ 2	$ 2
Credit losses for which an other-than-temporary impairment was not previously recognized	15	0	15	0
Ending balance	$ 17	$ 2	$ 17	$ 2