Reinsurance - Effects of Reinsurance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Premiums Earned, Net [Abstract]
Direct	$ 30,755	$ 29,812	$ 27,215
Assumed	384	400	602
Ceded	(513)	(570)	(603)
Premiums Earned Net	30,626	29,642	27,214
Reinsurance Recoveries [Abstract]
Reinsurance recoveries	540	737	658
Individual Life Insurance And Annuity Business Sold [Member]
Reinsurance Recoveries [Abstract]
Reinsurance recoveries	279	301	366
Other Subsegments [Member]
Reinsurance Recoveries [Abstract]
Reinsurance recoveries	261	436	292
Short Duration Contracts [Member]
Premiums Earned, Net [Abstract]
Direct	27,496	26,751	24,294
Assumed	247	289	429
Ceded	(229)	(254)	(226)
Premiums Earned Net	27,514	26,786	24,497
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	3,259	3,061	2,921
Assumed	137	111	173
Premiums Earned Net	3,112	2,856	2,717
Long Duration Contracts [Member] | Individual Life Insurance And Annuity Business Sold [Member]
Premiums Earned, Net [Abstract]
Ceded	(153)	(158)	(254)
Long Duration Contracts [Member] | Other Subsegments [Member]
Premiums Earned, Net [Abstract]
Ceded	$ (131)	$ (158)	$ (123)