Organization and Significant Accounting Policies - Narrative (Details) $ / shares in Units, $ in Millions	3 Months Ended			12 Months Ended
	Jun. 29, 2025 USD ($)	Dec. 31, 2024 USD ($)	Mar. 31, 2024 USD ($)	Dec. 31, 2025 USD ($) segment contract $ / shares	Dec. 31, 2024 USD ($) $ / shares	Dec. 31, 2023 USD ($) $ / shares
Accounting Policies [Abstract]
Number of business segments | segment				4
Number of contract types | contract				3
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Ending backlog				$ 193,600
Significant Accounting Policies [Line Items]
Goodwill		$ 11,067		11,314	$ 11,067	$ 10,799
Contract liabilities		9,795		11,440	9,795
Program losses				1,615	1,965	45
Independent research and development costs charged to cost of sales				$ 2,000	1,600	1,500
Number of years over which equity awards vest				1 year
Capitalized software		1,866		$ 2,417	1,866
Capitalized internal-use software accumulated amortization		3,100		3,400	3,100
Capitalized internal-use software amortization				393	346	263
Carrying amount of investments held in Lockheed martin venture fund		600		669	600
Realized (loss) gain reflected in other non-operating income				55	22	(64)
Realized (loss) gain recognized for changes in fair value, net of tax				$ 41	$ 17	$ (48)
Realized (loss) gain, net of tax, amount per share ( in dollars per share) | $ / shares				$ 0.18	$ 0.07	$ (0.19)
Equity method investments		654		$ 653	$ 654
Net earnings from equity method investments				$ 28	56	$ 40
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]				Other noncurrent assets
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]				Other noncurrent liabilities
Environmental costs eligible for future recovery				20 years
Derivative Asset, Statement of Financial Position [Extensible Enumeration]				Other current assets, Other noncurrent assets
Derivative Liability, Statement of Financial Position [Extensible Enumeration]				Other current liabilities, Other noncurrent liabilities
Minimum
Significant Accounting Policies [Line Items]
Number of years over which equity awards vest				1 year
Acquired finite-lived intangible assets are amortized				3 years
Minimum | Buildings
Significant Accounting Policies [Line Items]
Property, plant and equipment, estimated life				10 years
Minimum | Machinery and equipment
Significant Accounting Policies [Line Items]
Property, plant and equipment, estimated life				5 years
Minimum | Capitalized Software
Significant Accounting Policies [Line Items]
Property, plant and equipment, estimated life				2 years
Maximum
Significant Accounting Policies [Line Items]
Number of years over which equity awards vest				3 years
Acquired finite-lived intangible assets are amortized				20 years
Maximum | Buildings
Significant Accounting Policies [Line Items]
Property, plant and equipment, estimated life				40 years
Maximum | Machinery and equipment
Significant Accounting Policies [Line Items]
Property, plant and equipment, estimated life				15 years
Maximum | Capitalized Software
Significant Accounting Policies [Line Items]
Property, plant and equipment, estimated life				15 years
Restricted Stock Units and Performance Stock Units
Significant Accounting Policies [Line Items]
Number of years over which equity awards vest				3 years
Aeronautics
Significant Accounting Policies [Line Items]
Goodwill		196		$ 196	196	196
RMS
Significant Accounting Policies [Line Items]
Goodwill		6,712		6,737	6,712	6,741
Space
Significant Accounting Policies [Line Items]
Net earnings from equity method investments				5	45	20
MFC
Significant Accounting Policies [Line Items]
Goodwill		2,085		2,089	2,085	2,086
Favorable profit adjustments					155
Classified Program | Aeronautics
Significant Accounting Policies [Line Items]
Reach-forward loss				950	555
Favorable profit adjustments				90
Contract liabilities				495
Classified Program | Aeronautics | Initial Phase
Significant Accounting Policies [Line Items]
Reach-forward loss	$ 950
Cumulative losses on development				1,800
Classified Program | MFC
Significant Accounting Policies [Line Items]
Reach-forward loss		$ 1,310	$ 100		$ 1,400
Cumulative losses on development				1,460
Contract liabilities				1,190
Canadian Maritime Helicopter Program | RMS
Significant Accounting Policies [Line Items]
Reach-forward loss				570		100
Favorable profit adjustments						$ 65
Cumulative losses on development				670
Program losses	570
Contract assets				625
Türkish Utility Helicopter Program
Significant Accounting Policies [Line Items]
Cumulative losses on development				130
Program losses	95
Additional options of potential loss				115
Türkish Utility Helicopter Program | RMS
Significant Accounting Policies [Line Items]
Reach-forward loss				95
C-130 Programs | Aeronautics
Significant Accounting Policies [Line Items]
Favorable profit adjustments				140
Commercial Civil Space Program | Space
Significant Accounting Policies [Line Items]
Favorable profit adjustments				$ 130
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-01-01 | Period One
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation, percentage				37.00%
Expected time of satisfaction				12 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-01-01 | Period Two
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation, percentage				60.00%
Expected time of satisfaction				24 months
Amentum's Rapid Solutions
Significant Accounting Policies [Line Items]
Payments for acquisition	360
Goodwill	$ 195