Reinsurance - Effects of Reinsurance (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Premiums Earned, Net [Abstract]
Ceded	$ 113	$ 103	$ 380	$ 310
Premiums Earned Net	8,994	8,075	27,005	24,283
Reinsurance Recoveries [Abstract]
Reinsurance recoveries	140	95	300	277
Individual Life Insurance And Annuity Business Sold [Member]
Premiums Earned, Net [Abstract]
Ceded	32	33	103	105
Reinsurance Recoveries [Abstract]
Reinsurance recoveries	70	62	183	198
Other Subsegments [Member]
Premiums Earned, Net [Abstract]
Ceded	81	70	277	205
Reinsurance Recoveries [Abstract]
Reinsurance recoveries	$ 70	$ 33	$ 117	$ 79