Investments (Components of other-than-temporary impairment losses recognized in earnings) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Debt Securities, Available-for-sale [Line Items]
OTTI losses recognized in earnings	$ 3	$ 5	$ 9	$ 9
Corporate and other bonds
Debt Securities, Available-for-sale [Line Items]
OTTI losses recognized in earnings	1	4	6	8
Asset-backed
Debt Securities, Available-for-sale [Line Items]
OTTI losses recognized in earnings	$ 2	$ 1	$ 3	$ 1