Amount, after reinsurance, of paid claims and allocated claim adjustment expense used in claims development for short-duration insurance contracts. Excludes unallocated claim adjustment expense.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 50
-Paragraph 4B
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=65670685&loc=SL65671311-158438

Name:	us-gaap_ShortdurationInsuranceContractsCumulativePaidClaimsAndAllocatedClaimAdjustmentExpenseNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Medical Claims and Benefits Payable - Cumulative Paid Claims and Allocated Claims Adjustment Expenses (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Product Information [Line Items]
Claims paid	$ 42,014
Benefit Year 2015
Product Information [Line Items]
Claims paid	11,932	$ 11,906	$ 10,615
Benefit Year 2016
Product Information [Line Items]
Claims paid	14,952	$ 13,403
Benefit Year 2017
Product Information [Line Items]
Claims paid	$ 15,130