XML 97 R83.htm IDEA: XBRL DOCUMENT v3.20.4

Pension Plans and Postretirement Benefits - Plan Asset Allocations by Asset Category (Detail)	Dec. 31, 2020	Dec. 31, 2019
UNITED STATES | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Total	100.00%	100.00%
UNITED STATES | Pension Plan | Commingled and Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Total	29.00%	27.00%
UNITED STATES | Pension Plan | U.S. Government Securities
Defined Benefit Plan Disclosure [Line Items]
Total	28.00%	22.00%
UNITED STATES | Pension Plan | Fixed Income (excluding U.S. Government Securities)
Defined Benefit Plan Disclosure [Line Items]
Total	18.00%	33.00%
UNITED STATES | Pension Plan | Diversified Credit
Defined Benefit Plan Disclosure [Line Items]
Total	11.00%	5.00%
UNITED STATES | Pension Plan | Real Estate
Defined Benefit Plan Disclosure [Line Items]
Total	7.00%	7.00%
UNITED STATES | Pension Plan | Partnerships with Security Holdings
Defined Benefit Plan Disclosure [Line Items]
Total	4.00%	5.00%
UNITED STATES | Pension Plan | Other
Defined Benefit Plan Disclosure [Line Items]
Total	3.00%	1.00%
Canada | Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Total	100.00%	100.00%
Canada | Other Benefits | Equity Securities and Commingled Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Total	0.00%	35.00%
Canada | Other Benefits | Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Total	98.00%	62.00%
Canada | Other Benefits | Other
Defined Benefit Plan Disclosure [Line Items]
Total	2.00%	3.00%

X

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

X

- Definition

Percentage of actual investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

+ 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)(i)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

+ Details

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

X

- Details

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

X

- Details

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

X

- Details

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

X

- Details

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

X

- Details

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

X

- Details

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

X

- Details

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

X

- Details

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

X

- Details

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

X

- Details

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

X

- Details

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

X

- Details

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

X

- Details

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