Segment Information (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Revenues	$ 6,163	$ 1,871	$ 12,076	$ 3,801
Segment profit	876	120	1,555	226
Depreciation and amortization	368	145	609	297
Amortization of acquired intangible assets	169	22	289	36
Reconciliation of Consolidated Operating Income to Income Before Taxes [Abstract]
Profit	876	120	1,555	226
Interest Income	16	8	32	18
Interest expense	(78)	(29)	(154)	(54)
Restructuring costs	(192)	(25)	(382)	(82)
Amortization of acquired intangible assets	(169)	(22)	(289)	(36)
Transaction and integration-related costs	(66)	(53)	(190)	(109)
Income (loss) before income taxes	387	(1)	572	(37)
Operating segments
Segment Reporting Information [Line Items]
Revenues	6,163	1,871	12,076	3,801
Segment profit	958	171	1,607	332
Depreciation and amortization	342	129	560	265
Reconciliation of Consolidated Operating Income to Income Before Taxes [Abstract]
Profit	958	171	1,607	332
Operating segments \| GBS
Segment Reporting Information [Line Items]
Revenues	2,311	1,035	4,578	2,084
Segment profit	380	105	662	215
Depreciation and amortization	15	27	51	56
Reconciliation of Consolidated Operating Income to Income Before Taxes [Abstract]
Profit	380	105	662	215
Operating segments \| GIS
Segment Reporting Information [Line Items]
Revenues	3,142	836	6,111	1,717
Segment profit	469	66	759	117
Depreciation and amortization	298	102	474	209
Reconciliation of Consolidated Operating Income to Income Before Taxes [Abstract]
Profit	469	66	759	117
Operating segments \| USPS
Segment Reporting Information [Line Items]
Revenues	710	0	1,387	0
Segment profit	109	0	186	0
Depreciation and amortization	29	0	35	0
Reconciliation of Consolidated Operating Income to Income Before Taxes [Abstract]
Profit	109	0	186	0
All Other
Segment Reporting Information [Line Items]
Revenues	0	0	0	0
Segment profit	(82)	(51)	(52)	(106)
Depreciation and amortization	26	16	49	32
Reconciliation of Consolidated Operating Income to Income Before Taxes [Abstract]
Profit	$ (82)	$ (51)	$ (52)	$ (106)

Amortization Of Acquired Intangible Assets

No definition available.

Name:	csc_AmortizationOfAcquiredIntangibleAssets
Namespace Prefix:	csc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Depreciation And Amortization, Net Of Acquired Intangible Asset Amortization

+ References

No definition available.

+ Details

Name:	csc_DepreciationAndAmortizationNetOfAcquiredIntangibleAssetAmortization
Namespace Prefix:	csc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Reconciliation of consolidated operating income to income before taxes [Abstract]

+ References

No definition available.

+ Details

Name:	csc_ReconciliationOfConsolidatedOperatingIncomeToIncomeBeforeTaxesAbstract
Namespace Prefix:	csc_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Costs incurred to effect a business combination which have been expensed during the period. Such costs could include business integration costs, systems integration and conversion costs, and severance and other employee-related costs.

+ References

No definition available.

+ Details

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

- Definition

Amount, before tax, of income (loss) including portion attributable to noncontrolling interest. Includes, but is not limited to, income (loss) from continuing operations, discontinued operations and equity method investments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.18)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

+ Details

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

- Definition

Amount of the cost of borrowed funds accounted for as interest expense.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6450988&loc=d3e26243-108391

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28555-108399

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.9)
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

+ Details

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

- Definition

Amount of operating interest income, including, but not limited to, amortization and accretion of premiums and discounts on securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1(e))
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

+ Details

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

- Definition

The net result for the period of deducting operating expenses from operating revenues.

+ References

No definition available.

+ Details

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

- Definition

Amount of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 420
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 5.P.3)
-URI http://asc.fasb.org/extlink&oid=27011515&loc=d3e140864-122747

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 420
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6394359&loc=d3e17939-110869

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 420
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 5.P.4(b))
-URI http://asc.fasb.org/extlink&oid=27011515&loc=d3e140904-122747

+ Details

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

- Definition

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

+ Details

Name:	us-gaap_Revenues
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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

No definition available.

+ Details

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

- Details

Name:	us-gaap_ConsolidationItemsAxis=us-gaap_OperatingSegmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=csc_GBSSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=csc_GISSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=csc_UnitedStatesPublicSectorMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConsolidationItemsAxis=us-gaap_MaterialReconcilingItemsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: