Investments - Components of other-than-temporary impairment losses recognized in earnings (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
OTTI losses recognized in earnings	$ 2	$ 23
Corporate and other bonds
Schedule of Available-for-sale Securities [Line Items]
OTTI losses recognized in earnings	2	16
Residential mortgage-backed
Schedule of Available-for-sale Securities [Line Items]
OTTI losses recognized in earnings	0	0
Other asset-backed
Schedule of Available-for-sale Securities [Line Items]
OTTI losses recognized in earnings	0	2
Total asset-backed
Schedule of Available-for-sale Securities [Line Items]
OTTI losses recognized in earnings	0	2
Total fixed maturity securities available-for-sale
Schedule of Available-for-sale Securities [Line Items]
OTTI losses recognized in earnings	2	18
Equity securities available-for-sale -- Common stock
Schedule of Available-for-sale Securities [Line Items]
OTTI losses recognized in earnings	$ 0	$ 5