Goodwill and Intangible Assets (Schedule of Changes in the Carrying Amount of Goodwill) (Details) $ in Millions	3 Months Ended
	Jun. 30, 2017 USD ($)
Goodwill [Roll Forward]
March 31, 2017	$ 8,627	[1]
Acquisitions	7
Translation adjustments	4
June 30, 2017	8,638
Consumer Digital Safety
Goodwill [Roll Forward]
March 31, 2017	2,549
Acquisitions	2
Translation adjustments	1
June 30, 2017	2,552
Enterprise Security
Goodwill [Roll Forward]
March 31, 2017	6,078
Acquisitions	5
Translation adjustments	3
June 30, 2017	$ 6,086

[1] Derived from audited financial statements.