ACQUISITIONS - Narrative (Details) - USD ($) $ / shares in Units, shares in Millions				12 Months Ended
	Aug. 19, 2016	Oct. 07, 2015	Jul. 14, 2015	Mar. 31, 2017	Mar. 31, 2016	Aug. 20, 2017	Jul. 13, 2015	Mar. 31, 2015
Business Acquisition [Line Items]
Fair value of contingent liability				$ 5,449,000	$ 7,293,000
Increase (decrease) in goodwill				$ 1,718,162,000	1,709,369,000			$ 197,445,000
Weighted average useful life of acquired intangible assets				14 years 7 months 2 days
Backlog
Business Acquisition [Line Items]
Weighted average useful life of acquired intangible assets				2 years
Trademarks and trade names
Business Acquisition [Line Items]
Weighted average useful life of acquired intangible assets				8 years 6 months
Leasehold interest
Business Acquisition [Line Items]
Weighted average useful life of acquired intangible assets				5 years 7 months
Service Assurance reporting unit
Business Acquisition [Line Items]
Increase (decrease) in goodwill				$ 1,200,000,000	1,200,000,000
Security reporting unit
Business Acquisition [Line Items]
Increase (decrease) in goodwill				$ 548,500,000	547,400,000
Cash retention award | Vesting after August 4, 2015
Business Acquisition [Line Items]
Percent of cancelled Danaher equity awards replaced				50.00%
Restricted stock units | Vesting after August 4, 2015
Business Acquisition [Line Items]
Total equity consideration				$ 15,000,000
Percent of cancelled Danaher equity awards replaced				50.00%
Post combination compensation expense, Danaher equity awards | Vesting July 14, 2015 through August 4, 2015
Business Acquisition [Line Items]
Post combination compensation expense				$ 0	6,500,000
Post combination compensation expense, Danaher equity awards | Vesting after August 4, 2015
Business Acquisition [Line Items]
Post combination compensation expense				4,300,000	8,000,000
Post combination compensation expense, Danaher bonus
Business Acquisition [Line Items]
Post combination compensation expense				0	9,300,000
Post combination compensation expense, Danaher retention
Business Acquisition [Line Items]
Post combination compensation expense				$ 0	7,800,000
Common stock Voting
Business Acquisition [Line Items]
Share price (in dollars per share)							$ 36.89
Avvasi
Business Acquisition [Line Items]
Estimated purchase price	$ 4,606,000
Fair value of contingent liability	660,000
Increase (decrease) in goodwill	1,950,000
Decrease in prepaid expenses and other assets	(32,000)
Increase in inventory	85,000
Decrease in accounts payable	(1,000)
Increase in deferred revenue	$ 317,000
Weighted average useful life of acquired intangible assets	10 years 10 months 24 days
Avvasi | Service Assurance reporting unit
Business Acquisition [Line Items]
Increase (decrease) in goodwill	$ 2,000,000
Communications Business
Business Acquisition [Line Items]
Estimated purchase price		$ 5,700,000	$ 2,270,556,000
Increase (decrease) in goodwill		5,141,000	1,510,665,000
Total equity consideration		5,700,000	2,299,911,000
Decrease in prepaid expenses and other assets		(35,000)	(6,519,000)
Increase in deferred tax liabilities			348,004,000
Increase in inventory		78,000	80,719,000
Decrease in accounts payable		(8,000)	(21,311,000)
Decrease in accrued expenses		(176,000)	(12,916,000)
Increase in deferred revenue		$ 65,000	187,882,000
Weighted average useful life of acquired intangible assets				14 years 8 months
Revenues				$ 719,300,000
Net loss				2,100,000
Communications Business | General and administrative
Business Acquisition [Line Items]
Acquisition related costs				$ 0	$ 29,400,000
Communications Business | Developed technology
Business Acquisition [Line Items]
Weighted average useful life of acquired intangible assets				11 years 8 months 12 days
Communications Business | Customer relationships
Business Acquisition [Line Items]
Weighted average useful life of acquired intangible assets				16 years 3 months 18 days
Communications Business | Backlog
Business Acquisition [Line Items]
Weighted average useful life of acquired intangible assets				2 years
Communications Business | Trademarks and trade names
Business Acquisition [Line Items]
Weighted average useful life of acquired intangible assets				8 years 6 months
Communications Business | Leasehold interest
Business Acquisition [Line Items]
Weighted average useful life of acquired intangible assets				5 years 7 months 6 days
Communications Business | Service Assurance reporting unit
Business Acquisition [Line Items]
Increase (decrease) in goodwill			976,500,000
Communications Business | Security reporting unit
Business Acquisition [Line Items]
Increase (decrease) in goodwill			$ 534,800,000
Communications Business | Common stock Voting | Newco
Business Acquisition [Line Items]
Shares issued in business acquisition (in shares)			62.5
Communications Business | Immaterial error correction
Business Acquisition [Line Items]
Increase (decrease) in goodwill				$ (4,200,000)
Increase in inventory				200,000
Decrease in accounts payable				600,000
Decrease in accrued expenses				4,800,000
Increase in deferred revenue				1,400,000
Communications Business | Fair value adjustments
Business Acquisition [Line Items]
Increase (decrease) in goodwill				2,800,000
Decrease in prepaid expenses and other assets				200,000
Increase in deferred income taxes				700,000
Increase in deferred tax liabilities				$ 3,300,000
Forecast | Avvasi
Business Acquisition [Line Items]
Fair value of contingent liability						$ 660,000