Health Care Costs Payable - Components of Change in Health Care Costs Payable (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Sep. 30, 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	8,877
Health Care Benefits
Less: Claims paid
Benefit costs recorded in other insurance liabilities	45	$ 31
Corporate / Other
Less: Claims paid
Benefit costs recorded in other insurance liabilities	168	173
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	444
Add: Components of incurred health care costs
Current year	48,243	40,777
Prior years	(771)	(448)
Total incurred health care costs	47,472	40,329
Less: Claims paid
Current year	39,887	34,198
Prior years	6,639	5,865
Total claims paid	46,526	40,063
Add: Premium deficiency reserve	1	1
Health care costs payable, end of the period, net	8,873	7,585
Add: Reinsurance recoverables	4	8
Health care costs payable, end of the period	8,877	7,593
Premium deficiency reserve	$ 1	$ 1