Health Care Costs Payable - Narrative (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Liability for Claims and Claims Adjustment Expense [Line Items]
Incurred but not reported (IBNR) claims liability, net	$ 5,800
Health Insurance Product Line
Liability for Claims and Claims Adjustment Expense [Line Items]
Decrease in prior years' healthcare costs payable	$ (448)	$ (511)