DEBT - Credit Agreement (Details)	12 Months Ended
Dec. 31, 2019 USD ($)
Line of Credit \| Unsecured Revolving Credit Agreement \| Revolving Credit Facility
Debt Instrument [Line Items]
Debt instrument term (in years)	5 years
Maximum borrowing capacity	$ 2,000,000,000.0
Facility fee (percent)	0.15%
Debt to capitalization percentage, maximum	50.00%
Actual debt to capitalization percentage	32.00%
Maximum borrowing capacity including uncommitted incremental loan facility	$ 2,500,000,000
Uncommitted incremental loan facility	500,000,000
Line of credit, outstanding borrowings	0
Remaining borrowing capacity	$ 2,000,000,000
Line of Credit \| Unsecured Revolving Credit Agreement \| Revolving Credit Facility \| Minimum
Debt Instrument [Line Items]
Facility fee (percent)	0.09%
Line of Credit \| Unsecured Revolving Credit Agreement \| Revolving Credit Facility \| Maximum
Debt Instrument [Line Items]
Facility fee (percent)	0.25%
Line of Credit \| Unsecured Revolving Credit Agreement \| Revolving Credit Facility \| LIBOR
Debt Instrument [Line Items]
Basis points spread on variable rate (percent)	1.10%
Line of Credit \| Unsecured Revolving Credit Agreement \| Revolving Credit Facility \| LIBOR \| Minimum
Debt Instrument [Line Items]
Basis points spread on variable rate (percent)	0.91%
Line of Credit \| Unsecured Revolving Credit Agreement \| Revolving Credit Facility \| LIBOR \| Maximum
Debt Instrument [Line Items]
Basis points spread on variable rate (percent)	1.50%
Line of Credit \| Unsecured Revolving Credit Agreement \| Letter of Credit
Debt Instrument [Line Items]
Line of credit, outstanding borrowings	$ 0
Commercial paper
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 2,000,000,000

Debt Instrument, Covenant, Debt To Capitalization Percentage

No definition available.

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- Definition

Debt Instrument, Covenant, Debt To Capitalization Percentage, Maximum

+ References

No definition available.

+ Details

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- Definition

Maximum borrowing capacity under the credit facility including uncommitted incremental capacity and without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

No definition available.

+ Details

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Namespace Prefix:	hum_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line Of Credit Facility, Uncommitted Incremental Capacity

+ References

No definition available.

+ Details

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Namespace Prefix:	hum_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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- 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

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- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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- Definition

The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used.

+ References

No definition available.

+ Details

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

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Period Type:	instant

- Definition

The carrying value as of the balance sheet date of the current portion of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(13))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(19))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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- Details

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