Health Care Costs Payable - Components of Change in Health Care Costs Payable (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Health care costs payable, beginning of the period, net	$ 6,879
Less: Claims paid
Health care costs payable, end of the period, net	7,585
Health Insurance Product Line
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Health care costs payable, beginning of the period	6,879	$ 6,147
Less: Reinsurance recoverables	5	4
Health care costs payable, beginning of the period, net	6,874	6,143
Acquisition	412	0
Add: Components of incurred health care costs
Current year	14,764	13,804
Prior years	(464)	(446)
Total incurred health care costs	14,300	13,358
Less: Claims paid
Current year	8,773	8,004
Prior years	5,242	4,812
Total claims paid	14,015	12,816
Add: Premium deficiency reserve	10	11
Health care costs payable, end of the period, net	7,581	6,696
Add: Reinsurance recoverables	4	5
Health care costs payable, end of the period	7,585	6,701
Premium deficiency reserve	10	11
Health Care Benefits
Less: Claims paid
Benefit costs recorded in other insurance liabilities	9	10
Corporate / Other
Less: Claims paid
Benefit costs recorded in other insurance liabilities	$ 68	$ 80