Pensions and Postretirement Benefits Other Than Pensions (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Percent of our projected benefit obligation relates to plans that are not funded	5.00%
Deferred Compensation Liability, Current and Noncurrent	$ 15.1
Postemployment Benefits Obligation	7.6	$ 9.3
Postemployment Benefits, Period Expense	0.5	$ 1.4	$ 1.1
Pension Plans [Member]
Projected pension expense	11.4
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year	11.6
Postemployment Retirement Benefits [Member]
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	$ 1.0
United States
Discount rate	4.25%	3.58%
Accumulated benefit obligation for all defined benefit pension plans	$ 284.8	$ 304.9
Defined Contribution Plan, Cost	14.4	14.0	13.3
United States \| Pension Plans [Member]
Defined benefit plan, fair value of pension plan assets	259.4	283.2	202.4
Fair value of plan assets	259.4	283.2
Defined Benefit Plan, Plan Assets, Contributions by Employer	6.1	55.7	7.9
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	17.0
United States \| Fixed Income Investments [Member]
Defined benefit plan, fair value of pension plan assets	183.9	207.7
United States \| Fixed Income Investments [Member] \| Fair Value, Inputs, Level 1 [Member]
Defined benefit plan, fair value of pension plan assets	$ 0.0	$ 0.0
Non-US
Discount rate	2.76%	2.45%
Accumulated benefit obligation for all defined benefit pension plans	$ 349.1	$ 388.3
Defined Contribution Plan, Cost	8.0	7.0	5.6
Non-US \| Pension Plans [Member]
Defined benefit plan, fair value of pension plan assets	352.2	398.4	353.4
Fair value of plan assets	8.8	7.9
Defined Benefit Plan, Plan Assets, Contributions by Employer	5.4	5.2	$ 6.0
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	16.9
Non-US \| Fixed Income Investments [Member]
Defined benefit plan, fair value of pension plan assets	141.1	176.9
Non-US \| Fixed Income Investments [Member] \| Fair Value, Inputs, Level 1 [Member]
Defined benefit plan, fair value of pension plan assets	$ 0.0	0.0
Discretionary cotribution [Member] \| United States \| Pension Plans [Member]
Defined Benefit Plan, Plan Assets, Contributions by Employer		$ 50.0

Percent Of Our Projected Benefit Obligation Relates To Plans That Cannot Be Funded

No definition available.

Name:	alle_PercentOfOurProjectedBenefitObligationRelatesToPlansThatCannotBeFunded
Namespace Prefix:	alle_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Projected amount of pension benefit costs expected to be recognized during the next fiscal year for (1) defined benefit plans and (2) defined contribution plans. For defined benefit plans, pension expense includes the following components: service cost, interest cost, expected return on plan assets, gain (loss) on plan assets, prior service cost or credit, transition asset or obligation, and gain (loss) due to settlements or curtailments. For defined contribution plans, the pension expense generally equals the firm's contribution to employees' accounts (if the firm contributes) during the period.

+ References

No definition available.

+ Details

Name:	alle_ProjectedPensionExpense
Namespace Prefix:	alle_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Aggregate carrying value as of the balance sheet date of the liabilities for all deferred compensation arrangements. Represents currently earned compensation under compensation arrangements that is not actually paid until a later date.

+ References

No definition available.

+ Details

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

- Definition

Amount of actuarial present value of benefits attributed to employee service rendered, excluding assumptions about future compensation level.

+ References

+ Details

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

- Definition

Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan.

+ References

+ Details

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

- Definition

Amount of contribution received by defined benefit plan from employer which increases plan assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(5)(ii)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2709-114920

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(5)(iv)(01)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

+ Details

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

- Definition

Amount of benefits for defined benefit plan expected to be paid in next fiscal year following latest fiscal year.

+ References

+ Details

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

- Definition

Amount of contributions expected to be received by defined benefit plan from employer in next fiscal year following latest fiscal year.

+ References

+ Details

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

- Definition

Fair value of assets that have been segregated and restricted to provide pension or postretirement benefits. Assets include, but are not limited to, stocks, bonds, other investments, earnings from investments, and contributions by the employer and employees.

+ References

+ Details

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

- Definition

Fair value of plan assets for defined benefit pension plan with accumulated benefit obligation in excess of plan assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2417-114920

+ Details

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

- Definition

Amount of cost for defined contribution plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 70
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942

+ Details

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

- Definition

The carrying amount as of the balance sheet date of the obligations recognized for the various benefits provided to former or inactive employees, their beneficiaries, and covered dependents after employment but before retirement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 712
-SubTopic 10
-Section 25
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6410138&loc=d3e79691-111665

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 712
-SubTopic 10
-Section 25
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6410138&loc=d3e79708-111665

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.15)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.15)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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

- Definition

Period expense related to postemployment benefits.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_RetirementPlanTypeAxis=us-gaap_PensionPlansDefinedBenefitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RetirementPlanTypeAxis=us-gaap_PostemploymentRetirementBenefitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementGeographicalAxis=country_US
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_FixedIncomeInvestmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementGeographicalAxis=us-gaap_NonUsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=alle_DiscretionarycotributionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: