Health Care Costs Payable - Components of Change in Health Care Costs Payable (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Health care costs payable, beginning of the period, net	$ 7,936
Less: Claims paid
Health care costs payable, end of the period, net	8,272
Health Care Benefits
Less: Claims paid
Benefit costs recorded in other insurance liabilities	13	$ 9
Corporate / Other
Less: Claims paid
Benefit costs recorded in other insurance liabilities	45	68
Health Insurance Product Line
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Health care costs payable, beginning of the period	7,936	6,879
Less: Reinsurance recoverables	10	5
Health care costs payable, beginning of the period, net	7,926	6,874
Acquisition	0	412
Add: Components of incurred health care costs
Current year	16,291	14,764
Prior years	(652)	(464)
Total incurred health care costs	15,639	14,300
Less: Claims paid
Current year	9,538	8,773
Prior years	5,767	5,242
Total claims paid	15,305	14,015
Add: Premium deficiency reserve	7	10
Health care costs payable, end of the period, net	8,267	7,581
Add: Reinsurance recoverables	5	4
Health care costs payable, end of the period	8,272	7,585
Premium deficiency reserve	$ 7	$ 10