Health Care Costs Payable - Components of Change in Health Care Costs Payable (Details) $ in Millions	9 Months Ended
	Sep. 30, 2019 USD ($)
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Health care costs payable, beginning of the period, net	$ 6,147
Less: Claims paid
Health care costs payable, end of period, net	7,014
Health Insurance Product Line
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Health care costs payable, beginning of the period	6,147
Less: Reinsurance recoverables	4
Health care costs payable, beginning of the period, net	6,143
Add: Components of incurred health care costs
Current year	39,657
Prior years	(511)
Total incurred health care costs	39,146
Less: Claims paid
Current year	33,032
Prior years	5,253
Total claims paid	38,285
Add: Premium deficiency reserve	6
Health care costs payable, end of period, net	7,010
Add: Reinsurance recoverables	4
Health care costs payable, end of period	7,014
Premium deficiency reserve	6
Health Care Benefits Segment
Less: Claims paid
Benefit costs recorded in other insurance liabilities	31
Corporate / Other
Less: Claims paid
Benefit costs recorded in other insurance liabilities	$ 213