Health Care Costs Payable - Reconciliation of Health Care Costs Payable (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Health care costs payable, beginning of period, net	$ 6,879
Reclassification from pharmacy claims and discounts payable			$ 776
Less: Claims paid
Health care costs payable, end of period, net	7,936	$ 6,879
Health Care Benefits
Less: Claims paid
Benefit costs recorded in other insurance liabilities	41	41	4
Corporate/ Other
Less: Claims paid
Benefit costs recorded in other insurance liabilities	221	285	22
Health Insurance Product Line
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Health care costs payable, beginning of period	6,879	6,147	5
Less: Reinsurance recoverables	5	4	0
Health care costs payable, beginning of period, net	6,874	6,143	5
Acquisitions, net	414	0	5,357
Reclassification from pharmacy claims and discounts payable	0	0	776
Add: Components of incurred health care costs
Current year	55,835	52,723	6,594
Prior years	(429)	(524)	(42)
Total incurred health care costs	55,406	52,199	6,552
Less: Claims paid
Current year	48,770	46,158	6,303
Prior years	6,009	5,314	260
Total claims paid	54,779	51,472	6,563
Add: Premium deficiency reserve	11	4	16
Health care costs payable, end of period, net	7,926	6,874	6,143
Add: Reinsurance recoverables	10	5	4
Health care costs payable, end of period	$ 7,936	$ 6,879	$ 6,147