Acquisition (Schedule of Total Consideration) (Details) - USD ($) $ in Millions	Aug. 01, 2016	Sep. 30, 2016
Convertible Debt \| 2.0% Convertible Unsecured Notes due August 15, 2021
Business Acquisition [Line Items]
Stated interest rate (as a percent)		2.00%
Blue Coat, Inc.
Business Acquisition [Line Items]
Cash and equity consideration for outstanding Blue Coat common shares and restricted stock awards	$ 2,006
Cash consideration for outstanding Blue Coat debt	1,910
Issuance of Symantec 2.0% convertible debt to Bain Capital Funds (selling shareholder)	750
Fair value of vested assumed Blue Coat stock options	102
Cash consideration for acquiree acquisition-related expenses	51
Total consideration	4,819
Cash acquired	(146)
Net consideration transferred	$ 4,673
Blue Coat, Inc. \| Convertible Debt \| 2.0% Convertible Unsecured Notes due August 15, 2021
Business Acquisition [Line Items]
Stated interest rate (as a percent)	2.00%

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