Health Care Costs Payable - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Liability for Claims and Claims Adjustment Expense [Line Items]
Incurred but not reported (IBNR) claims liability, net	$ 5,700
Health Insurance Product Line
Liability for Claims and Claims Adjustment Expense [Line Items]
Decrease in prior years' healthcare costs payable	$ (464)	$ (446)