Fair Value (Narrative) (Details) - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018
Fair Value [Line Items]
Transfers Into Level 3	$ 0	$ 0
Transfers out of Level 3	0	0
Fair Value, Nonrecurring [Member]
Fair Value [Line Items]
Significant fair value adjustments for assets and liabilities measured on a nonrecurring basis	$ 0	$ 0

Fair Value Adjustments For Nonfinancial Assets And Liabilities Measured At Fair Value Or Financial Assets and Liabilities On Non Recurring Basis

No definition available.

+ Details

Name:	unh_FairValueAdjustmentsForNonfinancialAssetsAndLiabilitiesMeasuredAtFairValueOrFinancialAssetsandLiabilitiesNonRecurringBasis
Namespace Prefix:	unh_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy.

+ References

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsNonrecurringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: