Investments - Change in unrealized net capital gains and losses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Change in Unrealized Gain (Loss) Recognized in Accumulated Other Comprehensive Income (Loss)
Change in unrealized net capital gains and losses	$ 857	$ 745	$ (2,148)
Amounts recognized for:
Insurance reserves	(315)	0	28
DAC and DSI	(50)	(79)	112
Amounts recognized	(365)	(79)	140
Deferred income taxes	117	(233)	702
Increase (decrease) in unrealized net capital gains and losses, after-tax	609	433	(1,306)
EMA limited partnerships
Change in Unrealized Gain (Loss) Recognized in Accumulated Other Comprehensive Income (Loss)
Change in unrealized net capital gains and losses	5	0	1
Fixed income securities
Change in Unrealized Gain (Loss) Recognized in Accumulated Other Comprehensive Income (Loss)
Change in unrealized net capital gains and losses	204	516	(2,021)
Equity securities
Change in Unrealized Gain (Loss) Recognized in Accumulated Other Comprehensive Income (Loss)
Change in unrealized net capital gains and losses	651	233	(136)
Derivatives
Change in Unrealized Gain (Loss) Recognized in Accumulated Other Comprehensive Income (Loss)
Change in unrealized net capital gains and losses	$ (3)	$ (4)	$ 8