Global Health Care Medical Costs Payable - Activity (Details) - Global Health Benefits Segment [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Medical Claims Payable Activity [Abstract]
Beginning balance, unpaid claims, gross	$ 2,532	$ 2,355
Less: Reinsurance and other amounts recoverable	275	243
Beginning balance, unpaid claims, net	2,257	2,112
Incurred claims related to:
Current year	5,161	4,825
Prior years	(176)	(64)
Total incurred	4,985	4,761
Paid claims related to:
Current year	3,219	2,985
Prior years	1,509	1,449
Total paid	4,728	4,434
Ending balance, unpaid claims, net	2,514	2,439
Add: Reinsurance and other amounts recoverable	256	207
Ending balance, unpaid claims, gross	$ 2,770	$ 2,646