Reinsurance - Effects of Reinsurance (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Premiums Earned, Net [Abstract]
Ceded	$ 135	$ 120
Premiums Earned Net	8,999	8,151
Reinsurance Recoveries [Abstract]
Reinsurance recoveries	104	99
Individual Life Insurance And Annuity Business Sold [Member]
Premiums Earned, Net [Abstract]
Ceded	37	39
Reinsurance Recoveries [Abstract]
Reinsurance recoveries	57	70
Other Subsegments [Member]
Premiums Earned, Net [Abstract]
Ceded	98	81
Reinsurance Recoveries [Abstract]
Reinsurance recoveries	$ 47	$ 29