Activity in Benefits Payable (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Balances at January 1	$ 3,893	$ 3,775	$ 3,415
Acquisitions	0hum_BenefitsPayableAcquiredBalances	5hum_BenefitsPayableAcquiredBalances	66hum_BenefitsPayableAcquiredBalances
Current year, Incurred	38,641	32,711	30,198
Prior years, Incurred	(518)	(474)	(257)
Total incurred	38,123	32,237	29,941
Current year, Paid	(34,357)	(29,103)	(26,738)
Prior years, Paid	(3,262)	(3,021)	(2,909)
Total paid	(37,619)	(32,124)	(29,647)
Reinsurance recoverable	78	0	0
Balances at December 31	$ 4,475	$ 3,893	$ 3,775

Benefits payable amounts assumed from acquisition

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- Definition

Amount of payments to settle claims incurred in the current period and related claims settlement costs.

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Amount of payments to settle claims incurred in prior periods and related claims settlement costs.

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Amount of expense for claims incurred and costs incurred in the claim settlement process.

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Liability as of the balance sheet date for amounts representing estimated cost of settling unpaid claims under the terms of the underlying insurance policies, less estimated reinsurance recoveries on such claims. This includes an estimate for claims which have been incurred but not reported. Claim adjustment expenses represent the costs estimated to be incurred in the settlement of unpaid claims.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 40

-Section 50

-Paragraph 3

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Amount of payments to settle insured claims and pay costs incurred in the claims settlement process.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 25

-Subparagraph (g)

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Amount after valuation allowance recoverable under reinsurance contracts for claims and claims adjustments.

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Amount of expense for claims incurred in the current reporting period and related claims settlement costs.

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-Subparagraph (SX 210.12-18)

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Amount of expense for claims incurred in prior reporting periods and related claims settlement costs.

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