Debt Instrument, Covenant, Leverage Ratio, Achieved

No definition available.

Name:	alsn_DebtInstrumentCovenantLeverageRatioAchieved
Namespace Prefix:	alsn_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

Debt Instrument, Covenant, Leverage Ratio, Maximum

+ References

No definition available.

+ Details

Name:	alsn_DebtInstrumentCovenantLeverageRatioMaximum
Namespace Prefix:	alsn_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

Debt instrument covenant lien leverage ratio.

+ References

No definition available.

+ Details

Name:	alsn_DebtInstrumentCovenantLienLeverageRatio
Namespace Prefix:	alsn_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

Debt Instrument, Covenant, Net Leverage Ratio

+ References

No definition available.

+ Details

Name:	alsn_DebtInstrumentCovenantNetLeverageRatio
Namespace Prefix:	alsn_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

Debt instrument extended maturity year.

+ References

No definition available.

+ Details

Name:	alsn_DebtInstrumentExtendedMaturityYear
Namespace Prefix:	alsn_
Data Type:	xbrli:gYearItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt instrument floor rate.

+ References

No definition available.

+ Details

Name:	alsn_DebtInstrumentFloorRate
Namespace Prefix:	alsn_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt instrument maturity month and year.

+ References

No definition available.

+ Details

Name:	alsn_DebtInstrumentMaturityMonthAndYear
Namespace Prefix:	alsn_
Data Type:	xbrli:gYearMonthItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt instrument maturity year.

+ References

No definition available.

+ Details

Name:	alsn_DebtInstrumentMaturityYear
Namespace Prefix:	alsn_
Data Type:	xbrli:gYearItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt Issuance Expense

+ References

No definition available.

+ Details

Name:	alsn_DebtIssuanceExpense
Namespace Prefix:	alsn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

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

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=120520924&loc=SL6036836-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=119993939&loc=d3e28551-108399

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateEffectivePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

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

- Definition

Amount of the required periodic payments applied to principal.

+ References

+ Details

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

- Definition

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

+ Details

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

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

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

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions 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 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: 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(16))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

+ Details

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

- Definition

Maximum amount borrowed under the credit facility at any time during the period.

+ References

No definition available.

+ Details

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

- 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

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
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

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

- Definition

The fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=120520924&loc=SL6031897-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Reference 3: 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(16))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 4: 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(22))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=alsn_PriorTermLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=alsn_PriorRevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=alsn_NewRevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_LetterOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	alsn_VariableRateComponentAxis=alsn_VariableRateOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	alsn_VariableRateComponentAxis=alsn_VariableRateTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	alsn_VariableRateComponentAxis=alsn_VariableRateThreeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_BaseRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=alsn_NewSeniorSecuredCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=alsn_PriorSeniorSecuredCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=alsn_NewTermLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Debt - New Senior Secured Credit Facility - Additional Information (Details) - USD ($)	1 Months Ended	6 Months Ended
	Oct. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Mar. 31, 2019
Debt Instrument [Line Items]
Long-term debt		$ 2,816,000,000		$ 2,544,000,000
Deferred financing fees		$ 24,000,000		$ 26,000,000
Prior Term Loan
Debt Instrument [Line Items]
Long-term debt					$ 500,000,000
Debt instrument, due date		2022
Prior Revolving Credit Facility
Debt Instrument [Line Items]
Long-term debt					550,000,000
Debt instrument, due date		2021
New Revolving Credit Facility
Debt Instrument [Line Items]
Long-term debt					50,000,000
Debt instrument extended, due date		2024
Debt instrument, maturity month and year		2024-09
Credit facility, commitments amount		$ 600,000,000
Borrowing capacity at any time		500,000,000
Available revolving credit facility		319,000,000
Loans outstanding		$ 275,000,000
Commitment fee percentage		0.25%
Amount outstanding		$ 275,000,000
Achieved senior secured leverage ratio		0.56
New Revolving Credit Facility \| Letter of Credit
Debt Instrument [Line Items]
Credit facility, commitments amount		$ 75,000,000
Available revolving credit facility		$ 6,000,000
New Revolving Credit Facility \| LIBOR
Debt Instrument [Line Items]
Applicable margin over base rate		1.44%
New Revolving Credit Facility \| LIBOR \| First Lien Net Leverage Ratio is Above 4.00x
Debt Instrument [Line Items]
Applicable margin over base rate		1.75%
New Revolving Credit Facility \| LIBOR \| First Lien Net Leverage Ratio is Equal to or Less Than 4.00x and above 3.50x
Debt Instrument [Line Items]
Applicable margin over base rate		1.50%
New Revolving Credit Facility \| LIBOR \| First Lien Net Leverage Ratio is Equal to or Below 3.50x
Debt Instrument [Line Items]
Applicable margin over base rate		1.25%
New Revolving Credit Facility \| Base Rate \| First Lien Net Leverage Ratio is Above 4.00x
Debt Instrument [Line Items]
Applicable margin over base rate		0.75%
New Revolving Credit Facility \| Base Rate \| First Lien Net Leverage Ratio is Equal to or Less Than 4.00x and above 3.50x
Debt Instrument [Line Items]
Applicable margin over base rate		0.50%
New Revolving Credit Facility \| Base Rate \| First Lien Net Leverage Ratio is Equal to or Below 3.50x
Debt Instrument [Line Items]
Applicable margin over base rate		0.25%
New Revolving Credit Facility \| Minimum \| First Lien Net Leverage Ratio is Above 4.00x
Debt Instrument [Line Items]
Net leverage ratio		4.00
New Senior Secured Credit Facility
Debt Instrument [Line Items]
Debt instrument, due date		2022
Debt instrument extended, due date		2026
Deferred financing fees					$ 5,000,000
Debt issuance expense			$ 1,000,000
Required senior secured leverage ratio		5.50
Net leverage ratio		4.00
New Senior Secured Credit Facility \| Minimum \| First Lien Net Leverage Ratio is Equal to or Less Than 4.00x and above 3.50x
Debt Instrument [Line Items]
Net leverage ratio		3.50
New Senior Secured Credit Facility \| Maximum \| First Lien Net Leverage Ratio is Equal to or Less Than 4.00x and above 3.50x
Debt Instrument [Line Items]
Net leverage ratio		4.00
New Senior Secured Credit Facility \| Maximum \| First Lien Net Leverage Ratio is Equal to or Below 3.50x
Debt Instrument [Line Items]
Net leverage ratio		3.50
Prior Senior Secured Credit Facility
Debt Instrument [Line Items]
Deferred financing fees			$ 5,000,000
New Term Loan
Debt Instrument [Line Items]
Applicable margin over base rate	0.25%
Debt instrument effective interest rate		1.94%
Debt instrument, maturity month and year		2026-03
Principal payments on term loans		$ 2,000,000
New Term Loan \| LIBOR
Debt Instrument [Line Items]
Applicable margin over base rate		1.00%
New Term Loan \| Base Rate
Debt Instrument [Line Items]
Applicable margin over base rate		0.50%
New Term Loan \| Minimum \| LIBOR
Debt Instrument [Line Items]
Applicable margin over base rate		1.75%
New Term Loan \| Minimum \| Base Rate
Debt Instrument [Line Items]
Applicable margin over base rate		0.75%
Floor rate		1.00%