Global Health Care Medical Costs Payable (Details) - Global Health Benefits Segment [Member] - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015
Liability For Unpaid Claims And Claims Adjustment Expense [Line Items]
Incurred but not reported	$ 2,088		$ 1,960
Reported claims in process	542		506
Phyician incentives and other medical care expense and services payable	140		180
Total liability for unpaid claims and claims expenses	$ 2,770	$ 2,532	$ 2,646	$ 2,355