Liabilities for Unpaid Claims and Claims Expenses - Activity in Liabilities for Unpaid Claims and Claims Expenses (Details) - Group Disability and Life and Global Supplemental Benefits [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Liability For Unpaid Claims And Claims Adjustment Expense [Line Items]
Beginning balance, unpaid claims, gross	$ 4,809	$ 4,513	$ 4,726	$ 4,359
Less: Reinsurance and other amounts recoverable	123	115	121	115
Beginning balance, unpaid claims, net	4,686	4,398	4,605	4,244
Incurred claims related to:
Current year	1,076	1,124	2,224	2,112
Interest accretion	40	42	83	85
All other prior years	(7)	(19)	(71)	86
Total incurred	1,109	1,147	2,236	2,283
Paid claims related to:
Current year	703	683	1,074	1,010
Prior years	367	360	1,058	1,020
Total paid	1,070	1,043	2,132	2,030
Foreign currency	(3)	(4)	13	1
Ending balance, unpaid claims, net	4,722	4,498	4,722	4,498
Add: Reinsurance and other amounts recoverable	130	120	130	120
Ending balance, unpaid claims, gross	$ 4,852	$ 4,618	$ 4,852	$ 4,618