Business Segment Information - Revenues and Income From Continuing Operations by Segment (Details) - USD ($)	3 Months Ended
	Apr. 03, 2020	Sep. 27, 2019	Mar. 29, 2019
Segment Reporting Information [Line Items]
Revenue	$ 4,626,000,000		$ 1,728,000,000
Income From Continuing Operations Before Income Taxes
Non-operating income	(2,000,000)		(1,000,000)
Income from continuing operations before income taxes	221,000,000		283,000,000
Impairment of goodwill	301,000,000	$ 0
L3Harris
Segment Reporting Information [Line Items]
Revenue			1,728,000,000
Income From Continuing Operations Before Income Taxes
Amortization of acquisition-related intangibles	(158,000,000)
Additional cost of sales related to fair value step-up in inventory sold	15,000,000
Exelis
Income From Continuing Operations Before Income Taxes
Amortization of acquisition-related intangibles			(29,000,000)
Integrated Mission Systems
Income From Continuing Operations Before Income Taxes
Impairment of goodwill	0
Space and Airborne Systems
Income From Continuing Operations Before Income Taxes
Impairment of goodwill	5,000,000
Communication Systems
Income From Continuing Operations Before Income Taxes
Impairment of goodwill	0
Aviation Systems
Income From Continuing Operations Before Income Taxes
Impairment of goodwill	296,000,000
Other non-reportable business segments
Segment Reporting Information [Line Items]
Revenue	0		35,000,000
Operating segments | Integrated Mission Systems
Segment Reporting Information [Line Items]
Revenue	1,370,000,000		14,000,000
Income From Continuing Operations Before Income Taxes
Segment operating income	201,000,000		3,000,000
Operating segments | Space and Airborne Systems
Segment Reporting Information [Line Items]
Revenue	1,192,000,000		956,000,000
Income From Continuing Operations Before Income Taxes
Segment operating income	221,000,000		174,000,000
Operating segments | Communication Systems
Segment Reporting Information [Line Items]
Revenue	1,094,000,000		580,000,000
Income From Continuing Operations Before Income Taxes
Segment operating income	250,000,000		167,000,000
Operating segments | Aviation Systems
Segment Reporting Information [Line Items]
Revenue	1,011,000,000		144,000,000
Income From Continuing Operations Before Income Taxes
Segment operating income	(177,000,000)		17,000,000
Operating segments | Other non-reportable business segments
Income From Continuing Operations Before Income Taxes
Segment operating income	0		6,000,000
Corporate eliminations
Segment Reporting Information [Line Items]
Revenue	(41,000,000)		(1,000,000)
Unallocated corporate expenses
Income From Continuing Operations Before Income Taxes
Segment operating income	(33,000,000)		0
Additional cost of sales related to fair value step-up in inventory sold	15,000,000
Divestiture expenses	3,000,000
Segment reconciling items
Income From Continuing Operations Before Income Taxes
L3Harris Merger-related transaction and integration expenses	(31,000,000)		(16,000,000)
Amortization of acquisition-related intangibles	(145,000,000)		(25,000,000)
Pension adjustment	(97,000,000)		(47,000,000)
Non-operating income	95,000,000		46,000,000
Net interest expense	(63,000,000)		(42,000,000)
Segment reconciling items | L3Harris
Income From Continuing Operations Before Income Taxes
Amortization of acquisition-related intangibles	(120,000,000)
Segment reconciling items | Exelis
Income From Continuing Operations Before Income Taxes
Amortization of acquisition-related intangibles	(25,000,000)		$ (25,000,000)
Discontinued Operations, Held-for-sale or Disposed of by Sale | Applied Kilovolts and Analytical Instrumentation Business | Unallocated corporate expenses | Space and Airborne Systems
Income From Continuing Operations Before Income Taxes
Impairment of goodwill	$ 5,000,000