Investments - Change in unrealized net capital gains and losses (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Change in Unrealized Gain (Loss) Recognized in Accumulated Other Comprehensive Income (Loss)
Change in unrealized net capital gains and losses		$ (1,434)	$ 857	$ 745
Equity securities			1,160
Amounts recognized for:
Insurance reserves		315	(315)	0
DAC and DSI		163	(50)	(79)
Amounts recognized		478	(365)	(79)
Deferred income taxes	$ 202		117	(233)
(Decrease) increase in unrealized net capital gains and losses, after-tax		(754)	609	433
EMA limited partnerships
Change in Unrealized Gain (Loss) Recognized in Accumulated Other Comprehensive Income (Loss)
Change in unrealized net capital gains and losses		(1)	5	0
Fixed income securities
Change in Unrealized Gain (Loss) Recognized in Accumulated Other Comprehensive Income (Loss)
Change in unrealized net capital gains and losses		(1,431)	204	516
Equity securities
Change in Unrealized Gain (Loss) Recognized in Accumulated Other Comprehensive Income (Loss)
Change in unrealized net capital gains and losses		0	651	233
Derivatives
Change in Unrealized Gain (Loss) Recognized in Accumulated Other Comprehensive Income (Loss)
Change in unrealized net capital gains and losses		(2)	(3)	$ (4)
Accounting Standards Update 2016-01
Change in Unrealized Gain (Loss) Recognized in Accumulated Other Comprehensive Income (Loss)
Equity securities		$ 1,160	$ 1,160