Medical Costs Payable (Narrative) (Details) - USD ($) $ in Billions	Jun. 30, 2018	Dec. 31, 2017
Liability for Claims and Claims Adjustment Expense [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount	$ 13.5	$ 12.3

Estimated costs as of the balance sheet date of settling insured claims and costs incurred in the claims settlement process for claims that have not yet been submitted to the insurance company for reimbursement.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 5.W)
-URI http://asc.fasb.org/extlink&oid=27015833&loc=d3e570705-122907

Name:	us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredButNotReportedIBNRClaimsAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant