Investments - Components of other-than-temporary impairment losses recognized in earnings (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Schedule of Available-for-sale Securities [Line Items]
OTTI losses recognized in earnings	$ 2	$ 15	$ 4	$ 38
Corporate and other bonds
Schedule of Available-for-sale Securities [Line Items]
OTTI losses recognized in earnings	2	13	4	29
Residential mortgage-backed
Schedule of Available-for-sale Securities [Line Items]
OTTI losses recognized in earnings	0	1	0	1
Other asset-backed
Schedule of Available-for-sale Securities [Line Items]
OTTI losses recognized in earnings	0	1	0	3
Total asset-backed
Schedule of Available-for-sale Securities [Line Items]
OTTI losses recognized in earnings	0	2	0	4
Total fixed maturity securities available-for-sale
Schedule of Available-for-sale Securities [Line Items]
OTTI losses recognized in earnings	2	15	4	33
Equity securities available-for-sale -- Common stock
Schedule of Available-for-sale Securities [Line Items]
OTTI losses recognized in earnings	$ 0	$ 0	$ 0	$ 5