Acquisitions and Divestitures, Unaudited Pro Forma Statements of Operations Data (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	9 Months Ended
Sep. 29, 2017	Sep. 23, 2016	Sep. 29, 2017	Sep. 23, 2016
Acquisitions and Divestitures [Abstract]
Pro forma net sales	$ 2,659	$ 2,573	$ 8,097	$ 7,740
Pro forma income from continuing operations attributable to L3	23	148	388	462
Pro forma net income attributable to L3	$ 22	$ 148	$ 387	$ 525
Pro forma diluted earnings per share from continuing operations (in dollars per share)	$ 0.29	$ 1.88	$ 4.87	$ 5.87
Pro forma diluted earnings per share (in dollars per share)	$ 0.28	$ 1.88	$ 4.86	$ 6.67

The pro forma diluted net income per share for a period as if the business combination or combinations had been completed at the beginning of a period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(2)-(3)
-URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463

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Amount after tax of pro forma income from continuing operations as if the business combination had been completed at the beginning of a period.

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The pro forma net Income or Loss for the period as if the business combination or combinations had been completed at the beginning of a period.

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The pro forma revenue for a period as if the business combination or combinations had been completed at the beginning of the period.

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No definition available.

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Pro forma diluted earnings per share, which is commonly presented in initial public offerings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 855
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 1.B.3)
-URI http://asc.fasb.org/extlink&oid=6784503&loc=d3e463720-122850

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 270
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.10-01(b)(4))
-URI http://asc.fasb.org/extlink&oid=27015980&loc=d3e46468-122699

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 10
-Section S99
-Paragraph 7
-Subparagraph (SAB Topic 1.B.2)
-URI http://asc.fasb.org/extlink&oid=27047687&loc=d3e5934-122674

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

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