Insurance and Contractholder Liabilities - Integrated Medical - Activity (Details) - Integrated Medical - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning balance	$ 2,892
Beginning balance		$ 2,697
Less: Reinsurance and other amounts recoverable	303
Less: Reinsurance and other amounts recoverable		264
Beginning balance, net	2,589
Beginning balance, net		2,433
Incurred costs related to:
Current year	6,661	6,095
Prior years	(152)	(117)
Total incurred	6,509	5,978
Paid costs related to:
Current year	4,271	3,786
Prior years	2,027	1,908
Total paid	6,298	5,694
Ending balance, net	2,800
Ending balance, net		2,717
Add: Reinsurance and other amounts recoverable	200
Add: Reinsurance and other amounts recoverable		244
Ending balance	$ 3,000
Ending balance		$ 2,961