Reinsurance - Effects of Reinsurance (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Premiums Earned, Net [Abstract]
Ceded	$ 87	$ 113	$ 207	$ 249
Premiums Earned Net	8,010	7,654	16,113	15,400
Reinsurance Recoveries [Abstract]
Reinsurance recoveries	83	171	182	335
Individual Life Insurance And Annuity Business Sold [Member]
Premiums Earned, Net [Abstract]
Ceded	33	40	72	81
Reinsurance Recoveries [Abstract]
Reinsurance recoveries	66	66	136	134
Other Subsegments [Member]
Premiums Earned, Net [Abstract]
Ceded	54	73	135	168
Reinsurance Recoveries [Abstract]
Reinsurance recoveries	$ 17	$ 105	$ 46	$ 201