Health Care Costs Payable (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($)
Health care costs payable, beginning of the period	$ 6,147
Reinsurance recoverables	4
Health care costs payable, beginning of the period, net	6,143
Add Components Of Incurred Health Care Costs [Abstract]
Current year incurred health care costs	13,804
Prior year incurred health care costs	(446)
Policyholder Benefits and Claims Incurred, Net, Health	13,358
Less Claims Paid [Abstract]
Current year claims paid	8,004
Prior year claims paid	4,812
Total claims paid	12,816
Premium Deficiency Reserves	11
Health care costs payable, end of the period, net	6,696
Reinsurance recoverables	5
Health care costs payable, end of the period	6,701
Incurred but Not Reported (IBNR) Claims Liability, Net	5,100
Health Care Benefits Segment [Member]
Less Claims Paid [Abstract]
Benefit costs recorded in other insurance liabilities	10
Corporate / Other [Member]
Less Claims Paid [Abstract]
Benefit costs recorded in other insurance liabilities	$ 80