Investments (Components of other-than-temporary impairment losses recognized in earnings) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Debt Securities, Available-for-sale [Line Items]
OTTI losses recognized in earnings	$ 0	$ 2	$ 6	$ 4
Corporate and other bonds
Debt Securities, Available-for-sale [Line Items]
OTTI losses recognized in earnings	0	2	5	4
Asset-backed
Debt Securities, Available-for-sale [Line Items]
OTTI losses recognized in earnings	$ 0	$ 0	$ 1	$ 0