Employee plans - Summary of Changes in Level 3 Fair Value of Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Other Postretirement Plans
Change in plan assets
Fair value of plan assets at beginning of year	$ 7.6	$ 7.9
Fair value of plan assets at end of year	7.8	7.6
Other Postretirement Plans \| Insurance Contracts
Change in plan assets
Fair value of plan assets at beginning of year	7.6
Fair value of plan assets at end of year		7.6
Other Postretirement Plans \| Level 3 \| Insurance Contracts
Change in plan assets
Fair value of plan assets at beginning of year	7.6
Fair value of plan assets at end of year		7.6
U.S. Plans \| Other Postretirement Plans \| Insurance Contracts
Change in plan assets
Fair value of plan assets at end of year	7.8
U.S. Plans \| Other Postretirement Plans \| Level 3 \| Insurance Contracts
Change in plan assets
Fair value of plan assets at beginning of year	7.6	7.9
Realized gains (losses)	(0.4)	(0.2)
Purchases or acquisitions	0.6	0.2
Sales or dispositions	0.0	(0.3)
Currency and unrealized gains (losses) relating to instruments still held at December 31, 2018	0.0	0.0
Fair value of plan assets at end of year	7.8	7.6
U.S. Plans \| Pension Plans
Change in plan assets
Fair value of plan assets at beginning of year	3,578.4	3,452.1
Fair value of plan assets at end of year	3,112.8	3,578.4
U.S. Plans \| Pension Plans \| Level 3
Change in plan assets
Fair value of plan assets at beginning of year	0.0
Fair value of plan assets at end of year	0.0	0.0
International Plans \| Pension Plans
Change in plan assets
Fair value of plan assets at beginning of year	2,833.9	2,429.7
Fair value of plan assets at end of year	2,539.4	2,833.9
International Plans \| Pension Plans \| Insurance Contracts
Change in plan assets
Fair value of plan assets at beginning of year	135.8
Fair value of plan assets at end of year	123.7	135.8
International Plans \| Pension Plans \| Level 3
Change in plan assets
Fair value of plan assets at beginning of year	135.8
Fair value of plan assets at end of year	123.7	135.8
International Plans \| Pension Plans \| Level 3 \| Insurance Contracts
Change in plan assets
Fair value of plan assets at beginning of year	135.8	116.2
Realized gains (losses)	0.0	0.0
Purchases or acquisitions	3.5	10.8
Sales or dispositions	(11.7)	(11.4)
Currency and unrealized gains (losses) relating to instruments still held at December 31, 2018	(3.9)	20.2
Fair value of plan assets at end of year	$ 123.7	$ 135.8

Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from actual return (loss) on assets sold.

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

- Definition

Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from actual return (loss) on assets still held.

+ References

+ Details

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

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

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

- Definition

Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(iv)(01)
-URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(iv)(01)
-URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(ii)
-URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920

Reference 4: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 55
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=112275985&loc=d3e4179-114921

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920

Reference 6: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(ii)
-URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920

+ Details

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

- Definition

Amount, measured using unobservable input, of decrease in plan asset of defined benefit plan from sale.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(iv)(02)(B)
-URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920

+ Details

Name:	us-gaap_DefinedBenefitPlanPlanAssetsLevel3ReconciliationDecreaseForSale
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount, measured using unobservable input, of increase in plan asset of defined benefit plan from purchase.

+ References

+ Details

Name:	us-gaap_DefinedBenefitPlanPlanAssetsLevel3ReconciliationIncreaseForPurchase
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

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

- Details

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

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	us-gaap_RetirementPlanSponsorLocationAxis=us-gaap_ForeignPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: