Reinsurance - Effects of Reinsurance (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Premiums Earned, Net [Abstract]
Ceded	$ 132	$ 87	$ 267	$ 207
Premiums Earned Net	9,012	8,057	18,011	16,208
Reinsurance Recoveries [Abstract]
Reinsurance recoveries	56	83	160	182
Individual Life Insurance And Annuity Business Sold [Member]
Premiums Earned, Net [Abstract]
Ceded	34	33	71	72
Reinsurance Recoveries [Abstract]
Reinsurance recoveries	56	66	113	136
Other Subsegments [Member]
Premiums Earned, Net [Abstract]
Ceded	98	54	196	135
Reinsurance Recoveries [Abstract]
Reinsurance recoveries	$ 0	$ 17	$ 47	$ 46