Health Care Costs Payable - Components of Change in Health Care Costs Payable (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 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	7,362
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	26,390	26,864
Prior years	(420)	(489)
Total incurred health care costs	25,970	26,375
Less: Claims paid
Current year	20,223	20,552
Prior years	5,704	5,095
Total claims paid	25,927	25,647
Add: Premium deficiency reserve	29	14
Health care costs payable, end of the period, net	7,358	6,885
Add: Reinsurance recoverables	4	4
Health care costs payable, end of the period	7,362	6,889
Premium deficiency reserve	29	14
Health Care Benefits
Less: Claims paid
Benefit costs recorded in other insurance liabilities	20	21
Corporate / Other
Less: Claims paid
Benefit costs recorded in other insurance liabilities	$ 119	$ 136