Subsequent Events (Details) - Subsequent Event - Options outstanding - Chief Executive Officer $ in Millions	Oct. 26, 2021 USD ($)
Subsequent Event [Line Items]
Gross value of share options granted during the period	$ 150
Description of service or performance condition required to be met for earning right to award under share-based payment arrangement. Includes, but is not limited to, combination of market, performance or service condition.	2 years
Vesting, tranche one
Subsequent Event [Line Items]
Award vesting percentage	12.50%
Vesting, tranche two
Subsequent Event [Line Items]
Award vesting percentage	12.50%
Vesting, tranche three
Subsequent Event [Line Items]
Award vesting percentage	12.50%
Vesting, tranche four
Subsequent Event [Line Items]
Award vesting percentage	12.50%
Vesting, tranche five
Subsequent Event [Line Items]
Award vesting percentage	12.50%
Vesting, tranche six
Subsequent Event [Line Items]
Award vesting percentage	12.50%
Vesting, tranche seven
Subsequent Event [Line Items]
Award vesting percentage	12.50%
Vesting, tranche eight
Subsequent Event [Line Items]
Award vesting percentage	12.50%

Description of service or performance condition required to be met for earning right to award under share-based payment arrangement. Includes, but is not limited to, combination of market, performance or service condition.

No definition available.

+ Details

Name:	now_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingRightsBasedOnServicePerformanceAndMarketConditions
Namespace Prefix:	now_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Share-Based Compensation Arrangement By Share-Based Payment Award, Options, Grants in Period, Gross, Amount

+ References

No definition available.

+ Details

Name:	now_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGrossAmount
Namespace Prefix:	now_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Percentage of vesting of award under share-based payment arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_EmployeeStockOptionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_TitleOfIndividualAxis=srt_ChiefExecutiveOfficerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=us-gaap_ShareBasedCompensationAwardTrancheOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=us-gaap_ShareBasedCompensationAwardTrancheTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=us-gaap_ShareBasedCompensationAwardTrancheThreeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=now_ShareBasedPaymentArrangementTrancheFourMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=now_ShareBasedPaymentArrangementTrancheFiveMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=now_ShareBasedPaymentArrangementTrancheSixMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=now_ShareBasedPaymentArrangementTrancheSevenMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=now_ShareBasedPaymentArrangementTrancheEightMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: