Benefits costs incurred (reduced) for changes in estimated run-off of claims.

No definition available.

Name:	nsp_BenefitsCostsIncurredReducedRelatedtoRunoff
Namespace Prefix:	nsp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The decrease or increase in workers' compensation claims cost estimates for changes in the actuarial assumptions resulting from changes in actual claims experience and other trends.

+ References

No definition available.

+ Details

Name:	nsp_DecreaseIncreaseInAccruedWorkersCompensationCostsForChangesInEstimatedLosses
Namespace Prefix:	nsp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Carrying value of amounts transferred to third party workers' compensation insurance providers for security purposes that are expected to be returned or applied towards payment after one year or beyond the operating cycle, if longer.

+ References

No definition available.

+ Details

Name:	nsp_DepositsWorkersCompensation
Namespace Prefix:	nsp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The company's revenues are derived from its gross billings, which are based on the payroll cost of its worksite employees and a markup computed as a percentage of the payroll costs.

+ References

No definition available.

+ Details

Name:	nsp_GrossBillings
Namespace Prefix:	nsp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- References

No definition available.

+ Details

Name:	nsp_HealthInsuranceCostsAbstract
Namespace Prefix:	nsp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of days in advance of the beginning of a reporting quarter that United Healthcare establishes cash funding rates.

+ References

No definition available.

+ Details

Name:	nsp_NumberOfDaysInAdvanceOfBeginningOfReportingQuarterCarrierEstablishesCashFundingRates
Namespace Prefix:	nsp_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of our health insurance coverage provided by United

+ References

No definition available.

+ Details

Name:	nsp_PercentageofourhealthinsurancecoverageprovidedbyUnited
Namespace Prefix:	nsp_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The premiums owed to United which is included in accrued health insurance costs, a current liability in the Company's Consolidated Balance Sheet.

+ References

No definition available.

+ Details

Name:	nsp_PremiumsOwedToUnited
Namespace Prefix:	nsp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Carrying amount as of the balance sheet date for portion of health insurance contract to be utilized in one year of less.

+ References

No definition available.

+ Details

Name:	nsp_PrepaidHealthInsuranceCurrent
Namespace Prefix:	nsp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Total carrying amount as of the balance sheet date for health insurance contract.

+ References

No definition available.

+ Details

Name:	nsp_PrepaidHealthInsuranceCurrentAndNoncurrent
Namespace Prefix:	nsp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Carrying amount as of the balance sheet date for portion of health insurance contract to be utilized over longer than one year.

+ References

No definition available.

+ Details

Name:	nsp_PrepaidHealthInsuranceNoncurrent
Namespace Prefix:	nsp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the amount required to be held on deposit with United, which is determined as approximately one day of claims funding activity.

+ References

No definition available.

+ Details

Name:	nsp_RequiredDepositForHealthCareCosts
Namespace Prefix:	nsp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Revenue Composition [Abstract] Revenues are comprised of gross billings less worksite ("WSEE") payroll costs

+ References

No definition available.

+ Details

Name:	nsp_RevenueCompositionAbstract
Namespace Prefix:	nsp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Time period estimate of incurred claim costs to be paid included in long-term liabilities.

+ References

No definition available.

+ Details

Name:	nsp_TimePeriodEstimateOfIncurredClaimCostsToBePaidIncludedInLongTermLiabilities
Namespace Prefix:	nsp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Time period estimate of incurred claim costs to be paid included in short-term liabilities.

+ References

No definition available.

+ Details

Name:	nsp_TimePeriodEstimateOfIncurredClaimCostsToBePaidIncludedInShortTermLiabilities
Namespace Prefix:	nsp_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Time period incurred claims expected to be paid included in deposits.

+ References

No definition available.

+ Details

Name:	nsp_TimePeriodIncurredClaimsExpectedToBePaidIncludedInDeposits
Namespace Prefix:	nsp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Time period incurred claims expected to be paid recorded as restricted.

+ References

No definition available.

+ Details

Name:	nsp_TimePeriodIncurredClaimsExpectedToBePaidRecordedAsRestricted
Namespace Prefix:	nsp_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

U.S. Treasury rates that correspond with the weighted average estimated claim payout period utilized to discount workers' compensation cost estimates.

+ References

No definition available.

+ Details

Name:	nsp_USTreasuryRatesThatCorrespondWithWeightedAverageEstimatedClaimPayoutPeriod
Namespace Prefix:	nsp_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Unbilled amounts due for services rendered, net of customer prepayments of unbilled amounts.

+ References

No definition available.

+ Details

Name:	nsp_Unbilled
Namespace Prefix:	nsp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The liability as of the balance sheet date representing required funding mandated by statute or regulatory authority that is related directly or indirectly to underwriting activities, including pools for self-insurance and excluding premium taxes and income taxes. The funds derived from the assessments generally enable a government guarantor to pay insurance claims in the event that the underwriting insurer is insolvent or otherwise unable to meet its payment obligations.

+ References

No definition available.

+ Details

Name:	nsp_UndiscountedAccruedWorkersCompensationCosts
Namespace Prefix:	nsp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of workers' compensation - deposit funds held in trust accounts.

+ References

No definition available.

+ Details

Name:	nsp_WorkersCompDepositsHeldInTrust
Namespace Prefix:	nsp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Carrying value as of the balance sheet date of workers' compensation administrative fees.

+ References

No definition available.

+ Details

Name:	nsp_WorkersCompensationAdministrativeFeesAccrued
Namespace Prefix:	nsp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

+ Details

Name:	nsp_WorkersCompensationCostsAbstract
Namespace Prefix:	nsp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The change in worker's compensation reserve liability during the period resulting from the discount applied to reduce the reserve to present value.

+ References

No definition available.

+ Details

Name:	nsp_WorkersCompensationDiscountChangedDuringPeriod
Namespace Prefix:	nsp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Expense accrued pertaining to workers compensation costs.

+ References

No definition available.

+ Details

Name:	nsp_WorkersCompensationExpense
Namespace Prefix:	nsp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Carrying value as of the balance sheet date of obligations and payables pertaining to claims incurred of a workers compensation nature net of administrative fees. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer) net of administrative fees.

+ References

No definition available.

+ Details

Name:	nsp_WorkersCompensationLiabilityNetOfAdminFeesCurrent
Namespace Prefix:	nsp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The maximum amount the Company will bear of the economic burden per policy year for those claims exceeding the first layer maximum per claim occurrence.

+ References

No definition available.

+ Details

Name:	nsp_WorkersCompensationMaximumAggregateEconomicBurdenForClaimsInExcessOfFirstLayerCapPerPolicyYear
Namespace Prefix:	nsp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The Company's maximum economic burden for the first layer of claims per occurrence.

+ References

No definition available.

+ Details

Name:	nsp_WorkersCompensationMaximumEconomicBurdenFirstLayerOfClaimsPerOccurrence
Namespace Prefix:	nsp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Payroll costs incurred (including share-based compensation) by the company's worksite employees that are directly related to services rendered by the worksite employees during the reporting period.

+ References

No definition available.

+ Details

Name:	nsp_WorksiteEmployeePayrollCost
Namespace Prefix:	nsp_
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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-5

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 91
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479777/606-10-55-91

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 91
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479777/606-10-55-91

Reference 4: http://www.xbrl.org/2003/role/exampleRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 91
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479777/606-10-55-91

Reference 5: http://www.xbrl.org/2003/role/exampleRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 91
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479777/606-10-55-91

Reference 6: http://www.xbrl.org/2003/role/exampleRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 91
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479777/606-10-55-91

Reference 7: http://www.xbrl.org/2003/role/exampleRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 91
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479777/606-10-55-91

Reference 8: http://www.xbrl.org/2003/role/exampleRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 91
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479777/606-10-55-91

+ Details

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

- References

No definition available.

+ Details

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

- Definition

Sum of adjustments to the estimated reserve for unpaid claims and claims adjustment expense.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480081/944-40-50-3

+ Details

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

- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 25
-Subparagraph (g)
-SubTopic 10
-Topic 230
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-25

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 944
-SubTopic 40
-Name Accounting Standards Codification
-Section 55
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480046/944-40-55-7

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480081/944-40-50-3

+ Details

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

- Definition

Amount of cash and cash equivalents restricted as to withdrawal or usage, classified as current. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(1))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482913/230-10-50-8

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-4

+ Details

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

- References

No definition available.

+ Details

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

- Definition

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 41
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-41

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 270
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482964/270-10-50-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (ee)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-32

Reference 4: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-32

Reference 5: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-32

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 924
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 11.L)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479941/924-10-S99-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-5

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 30
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-30

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-42

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-22

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 40
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-40

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-22

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-4

+ Details

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

- Definition

Carrying value as of the balance sheet date of obligations and payables pertaining to claims incurred of a workers compensation nature.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(20))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(24))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(15)(5))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1

+ Details

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

- Definition

Carrying value as of the balance sheet date of obligations and payables pertaining to claims incurred of a workers compensation nature. Used to reflect the noncurrent portion of the liabilities (due beyond one year; or beyond one operating cycle if longer).

+ References

+ Details

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

- Details

Name:	srt_StatementGeographicalAxis=nsp_NortheastMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=nsp_SoutheastMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=nsp_CentralMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=nsp_SouthwestMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=nsp_WestMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=nsp_OtherRevenuesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Accounting Policies (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
Accounting Policies (Details) - USD ($) $ in Millions	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024	Dec. 31, 2024	Dec. 31, 2023	Oct. 01, 2019	Sep. 30, 2019
Revenue from Contract with Customer [Abstract]
Unbilled	$ 829.0		$ 829.0		$ 810.0
Disaggregation of Revenue [Line Items]
Revenues	1,658.0	$ 1,605.0	3,521.0	$ 3,407.0
Revenue Composition [Abstract]
Gross billings	10,558.0	10,361.0	22,702.0	21,844.0
Worksite employee payroll cost	8,900.0	8,756.0	19,181.0	18,437.0
Revenues	$ 1,658.0	1,605.0	$ 3,521.0	3,407.0
Health Insurance Costs [Abstract]
Percentage of our health insurance coverage provided by United	84.00%		84.00%
Number of days in advance of the beginning of a reporting quarter United establishes cash funding rates			90 days
Required accumulated cash surplus	$ 9.0		$ 9.0		9.0
Required deposit equal to approximately one day of claims funding activity	7.0		7.0
Prepaid health insurance, current	26.0		26.0
Amount which plan costs were less than the net premiums paid and owed	35.0		35.0
Premiums owed to United	(53.0)		(53.0)
Benefits costs incurred (reduced) related to run-off	11.0	(26.0)	11.0	(26.0)
Workers' Compensation Costs [Abstract]
Company's maximum economic burden for the first layer of claims per occurrence							$ 1.5	$ 1.0
Company's maximum aggregate economic burden for claims in excess of 1 million per policy year							$ 6.0	$ 6.0
Decrease Increase in accrued workers' compensation costs for changes in estimated losses			$ (14.0)	$ (17.0)
U.S. Treasury rates that correspond with the weighted average estimated claim payout period (in hundredths)			4.00%	4.50%
Incurred but not paid workers compensation liabilities [Abstract]
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustments					204.0	$ 220.0
Workers' Compensation Expense			$ 32.0	$ 31.0
Workers' Compensation Discount, Changed during period			(6.0)	(7.0)
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid			(41.0)	(33.0)
Workers' Compensation Liability	189.0	211.0	189.0	211.0
WorkersCompensationLiabilityNetOfAdminFeesCurrent	76.0	65.0	76.0	65.0
Workers' Compensation Liability, Noncurrent	113.0	146.0	113.0	146.0	135.0
Workers' Compensation Liability	189.0	211.0	189.0	211.0
Workers compensation administrative fees accrued	3.0	2.0	3.0	2.0
Undiscounted accrued workers' compensation costs			$ 228.0	244.0
Time period incurred claims expected to be paid recorded as restricted cash			1 year
Time period incurred claims expected to be paid included in deposits			Greater than 1 year
Restricted cash	76.0	64.0	$ 76.0	64.0	69.0	57.0
Deposits workers compensation	174.0	170.0	174.0	170.0	$ 178.0	$ 198.0
WorkersCompDepositsHeldInTrust	243.0		$ 243.0
Time period estimate of incurred claim costs to be paid included in short-term liabilities			1 year
Time period estimate of incurred claim costs to be paid included in long term liabilities			Greater than 1 year
Northeast [Member]
Disaggregation of Revenue [Line Items]
Revenues	452.0	437.0	$ 978.0	946.0
Revenue Composition [Abstract]
Revenues	452.0	437.0	978.0	946.0
Southeast [Member]
Disaggregation of Revenue [Line Items]
Revenues	238.0	225.0	495.0	471.0
Revenue Composition [Abstract]
Revenues	238.0	225.0	495.0	471.0
Central [Member]
Disaggregation of Revenue [Line Items]
Revenues	301.0	292.0	636.0	616.0
Revenue Composition [Abstract]
Revenues	301.0	292.0	636.0	616.0
Southwest [Member]
Disaggregation of Revenue [Line Items]
Revenues	311.0	304.0	658.0	644.0
Revenue Composition [Abstract]
Revenues	311.0	304.0	658.0	644.0
West [Member]
Disaggregation of Revenue [Line Items]
Revenues	339.0	329.0	716.0	695.0
Revenue Composition [Abstract]
Revenues	339.0	329.0	716.0	695.0
Other Revenues [Member]
Disaggregation of Revenue [Line Items]
Revenues	17.0	18.0	38.0	35.0
Revenue Composition [Abstract]
Revenues	$ 17.0	$ 18.0	$ 38.0	$ 35.0