Accounts Receivable, Net (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Accounts Receivable, Net [Abstract]
Insurance customer receivables	$ 2,433	$ 1,888
Noninsurance customer receivables	4,891	4,988
Pharmaceutical manufacturer receivable	3,953	3,321
Other receivables	442	276
Total accounts receivable, net	11,719	10,473
Pharmaceutical manufacturer receivables under noninsurance customer contracts	330	406
Allowance for doubtful accounts, customer credit allowances and contractual allowances	$ 720	$ 217