Global Health Care Medical Costs Payable - Prior Year Development (Details) - Global Health Benefits Segment [Member] - USD ($) $ in Millions	6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Abstract]
(Favorable) Unfavorable incurred costs related to prior years' claims payable	$ (83)		$ (210)
Incurred costs related to prior years' claims payable percentage	0.40%		1.30%
Favorable (unfavorable) impact of prior development on shareholders' net income		$ 44
Completion Factors [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Abstract]
Incurred costs related to prior years' claims payable percentage	0.30%		0.40%
Medical Cost Trend [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Abstract]
Incurred costs related to prior years' claims payable percentage	0.10%		0.70%
Reinsurance Reimbursements Under Health Care Reform [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Abstract]
Incurred costs related to prior years' claims payable percentage			0.20%