Global Health Care Medical Costs Payable - Activity (Details) - Global Health Benefits Segment [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Medical Claims Payable Activity [Abstract]
Balance at January 1,	$ 2,355	$ 2,180	$ 2,050
Less: Reinsurance and other amounts recoverable	243	252	194
Balance at January 1, net	2,112	1,928	1,856
Incurred claims related to:
Current year	19,087	18,564	16,853
Prior years	(78)	(210)	(159)
Total incurred	19,009	18,354	16,694
Paid claims related to:
Current year	17,052	16,588	14,966
Prior years	1,812	1,582	1,656
Total paid	18,864	18,170	16,622
Balance at December 31, net	2,257	2,112	1,928
Add: Reinsurance and other amounts recoverable	275	243	252
Balance at December 31,	$ 2,532	$ 2,355	$ 2,180