Business Segment Information - Revenues and Income From Continuing Operations by Segment (Details) - USD ($)	3 Months Ended			6 Months Ended
	Jul. 03, 2020	Sep. 27, 2019	Jun. 28, 2019	Jul. 03, 2020	Jun. 28, 2019
Segment Reporting Information [Line Items]
Revenue	$ 4,445,000,000		$ 1,865,000,000	$ 9,071,000,000	$ 3,593,000,000
Income From Continuing Operations Before Income Taxes
Non-operating income	7,000,000		2,000,000	5,000,000	1,000,000
Income from continuing operations before income taxes	336,000,000		302,000,000	557,000,000	585,000,000
Loss on sale of business				52,000,000	0
Non-cash remeasurement loss on potential divestiture				14,000,000
Impairment of goodwill		$ 0		369,000,000
Restructuring charges				22,000,000
L3Harris
Segment Reporting Information [Line Items]
Revenue			1,865,000,000		3,593,000,000
Income From Continuing Operations Before Income Taxes
Amortization of acquisition-related intangibles	(209,000,000)			(367,000,000)
Additional cost of sales related to the fair value step-up in inventory sold	16,000,000		0	31,000,000	0
Restructuring charges	7,000,000			7,000,000
Exelis
Income From Continuing Operations Before Income Taxes
Amortization of acquisition-related intangibles			(27,000,000)		(56,000,000)
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				364,000,000
Other non-reportable business segments
Segment Reporting Information [Line Items]
Revenue	0		44,000,000	0	79,000,000
Operating segments | Integrated Mission Systems
Segment Reporting Information [Line Items]
Revenue	1,331,000,000		11,000,000	2,701,000,000	25,000,000
Income From Continuing Operations Before Income Taxes
Segment operating income	224,000,000		3,000,000	425,000,000	6,000,000
Operating segments | Space and Airborne Systems
Segment Reporting Information [Line Items]
Revenue	1,249,000,000		1,019,000,000	2,441,000,000	1,975,000,000
Income From Continuing Operations Before Income Taxes
Segment operating income	235,000,000		195,000,000	456,000,000	369,000,000
Operating segments | Communication Systems
Segment Reporting Information [Line Items]
Revenue	1,112,000,000		609,000,000	2,206,000,000	1,189,000,000
Income From Continuing Operations Before Income Taxes
Segment operating income	265,000,000		176,000,000	515,000,000	343,000,000
Operating segments | Aviation Systems
Segment Reporting Information [Line Items]
Revenue	800,000,000		186,000,000	1,811,000,000	330,000,000
Income From Continuing Operations Before Income Taxes
Segment operating income	31,000,000		19,000,000	(146,000,000)	36,000,000
Operating segments | Other non-reportable business segments
Income From Continuing Operations Before Income Taxes
Segment operating income	0		8,000,000	0	14,000,000
Corporate eliminations
Segment Reporting Information [Line Items]
Revenue	(47,000,000)		(4,000,000)	(88,000,000)	(5,000,000)
Unallocated corporate expenses
Income From Continuing Operations Before Income Taxes
Segment operating income	(116,000,000)		(1,000,000)	(149,000,000)	(1,000,000)
Divestiture-related expenses	58,000,000			61,000,000
Loss on sale of business				26,000,000
Non-cash adjustment to gain on sale of business				12,000,000
Impairment of goodwill	14,000,000
Unallocated corporate expenses | L3Harris
Income From Continuing Operations Before Income Taxes
Additional cost of sales related to the fair value step-up in inventory sold	16,000,000			31,000,000
Restructuring charges				7,000,000
Unallocated corporate expenses | Disposal Group, Held-for-sale, Not Discontinued Operations | Applied Kilovolts and Analytical Instrumentation Business
Income From Continuing Operations Before Income Taxes
Impairment of goodwill				5,000,000
Segment reconciling items
Income From Continuing Operations Before Income Taxes
L3Harris Merger-related transaction and integration expenses	(37,000,000)		(36,000,000)	(68,000,000)	(52,000,000)
Amortization of acquisition-related intangibles	(208,000,000)		(25,000,000)	(353,000,000)	(50,000,000)
Pension adjustment	(98,000,000)		(46,000,000)	(195,000,000)	(93,000,000)
Non-operating income	105,000,000		48,000,000	200,000,000	94,000,000
Net interest expense	(65,000,000)		(39,000,000)	(128,000,000)	(81,000,000)
Segment reconciling items | L3Harris
Income From Continuing Operations Before Income Taxes
Amortization of acquisition-related intangibles	(183,000,000)			(303,000,000)
Segment reconciling items | Exelis
Income From Continuing Operations Before Income Taxes
Amortization of acquisition-related intangibles	$ (25,000,000)		$ (50,000,000)	$ (25,000,000)	$ (50,000,000)