Investments - Components of other-than-temporary impairment losses recognized in earnings (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Schedule of Available-for-sale Securities [Line Items]
OTTI losses recognized in earnings	$ 5	$ 18	$ 9	$ 56
Corporate and other bonds
Schedule of Available-for-sale Securities [Line Items]
OTTI losses recognized in earnings	4	14	8	43
Residential mortgage-backed
Schedule of Available-for-sale Securities [Line Items]
OTTI losses recognized in earnings	1	0	1	1
Other asset-backed
Schedule of Available-for-sale Securities [Line Items]
OTTI losses recognized in earnings	0	0	0	3
Total asset-backed
Schedule of Available-for-sale Securities [Line Items]
OTTI losses recognized in earnings	1	0	1	4
Total fixed maturity securities available-for-sale
Schedule of Available-for-sale Securities [Line Items]
OTTI losses recognized in earnings	5	14	9	47
Equity securities available-for-sale -- Common stock
Schedule of Available-for-sale Securities [Line Items]
OTTI losses recognized in earnings	$ 0	$ 4	$ 0	$ 9