Reinsurance - Effects of Reinsurance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Premiums Earned, Net [Abstract]
Premiums Earned Net	$ 36,113	$ 32,491	$ 30,824
Reinsurance Recoveries [Abstract]
Reinsurance recoveries	452	325	540
Individual Life Insurance And Annuity Business Sold [Member]
Reinsurance Recoveries [Abstract]
Reinsurance recoveries	249	259	279
Other Subsegments [Member]
Reinsurance Recoveries [Abstract]
Reinsurance recoveries	203	66	261
Short Duration Contracts [Member]
Premiums Earned, Net [Abstract]
Direct	32,148	28,838	27,694
Assumed	77	199	247
Ceded	(182)	(150)	(229)
Premiums Earned Net	32,043	28,887	27,712
Premiums Written, Net [Abstract]
Direct premiums, written versus earned
Assumed premiums, written versus earned
Ceded premiums, written versus earned
Net premiums, written versus earned
Long Duration Contracts [Member]
Premiums Earned, Net [Abstract]
Direct	4,268	3,748	3,259
Assumed	116	130	137
Premiums Earned Net	4,070	3,604	3,112
Long Duration Contracts [Member] | Individual Life Insurance And Annuity Business Sold [Member]
Premiums Earned, Net [Abstract]
Ceded	(133)	(143)	(153)
Long Duration Contracts [Member] | Other Subsegments [Member]
Premiums Earned, Net [Abstract]
Ceded	$ (181)	$ (131)	$ (131)