Reinsurance - Effects of Reinsurance (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Premiums Earned, Net [Abstract]
Ceded	$ 103	$ 131	$ 310	$ 380
Premiums Earned Net	8,030	7,605	24,143	23,005
Reinsurance Recoveries [Abstract]
Reinsurance recoveries	95	85	277	420
Individual Life Insurance And Annuity Business Sold [Member]
Premiums Earned, Net [Abstract]
Ceded	33	37	105	118
Reinsurance Recoveries [Abstract]
Reinsurance recoveries	62	77	198	211
Other Subsegments [Member]
Premiums Earned, Net [Abstract]
Ceded	70	94	205	262
Reinsurance Recoveries [Abstract]
Reinsurance recoveries	$ 33	$ 8	$ 79	$ 209