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		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Liability For Unpaid Claims And Claims Adjustment Expense [Line Items]
Beginning balance, unpaid claims, gross	$ 4,852	$ 4,618	$ 4,726	$ 4,359
Less: Reinsurance and other amounts recoverable	130	120	121	115
Beginning balance, unpaid claims, net	4,722	4,498	4,605	4,244
Incurred claims related to:
Current year	1,066	1,046	3,290	3,158
Interest accretion	36	40	119	125
All other prior years	12	4	(59)	90
Total incurred	1,114	1,090	3,350	3,373
Paid claims related to:
Current year	806	761	1,880	1,771
Prior years	269	275	1,327	1,295
Total paid	1,075	1,036	3,207	3,066
Foreign currency	0	7	13	8
Ending balance, unpaid claims, net	4,761	4,559	4,761	4,559
Add: Reinsurance and other amounts recoverable	134	121	134	121
Ending balance, unpaid claims, gross	$ 4,895	$ 4,680	$ 4,895	$ 4,680