Insurance and Contractholder Liabilities - Other Segments - Activity in Liabilities for Unpaid Claims and Claims Expenses (Details) - Intenational Markets and Global Disability and Life [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Liability For Unpaid Claims And Claims Adjustment Expense [Line Items]
Beginning balance, unpaid claims, gross	$ 5,274	$ 4,997	$ 4,609
Less: Reinsurance and other amounts recoverable	140	123	121
Beginning balance, unpaid claims, net	5,134	4,874	4,488
Incurred claims related to:
Current year	5,350	5,097	5,116
Interest accretion	156	163	161
All other prior years	(147)	(43)	85
Total incurred	5,359	5,217	5,362
Paid claims related to:
Current year	3,391	3,229	3,221
Prior years	1,808	1,757	1,739
Total paid	5,199	4,986	4,960
Acquisitions	23	0	0
Foreign currency	(41)	29	(16)
Ending balance, unpaid claims, net	5,276	5,134	4,874
Add: Reinsurance and other amounts recoverable	156	140	123
Ending balance, unpaid claims, gross	$ 5,432	$ 5,274	$ 4,997