Equity Award Plans - Narrative (Details) - USD ($)			1 Months Ended		12 Months Ended
	Jan. 01, 2016	Dec. 30, 2013	May. 31, 2014	Dec. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Jan. 01, 2015	Mar. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
General vesting period					4 years
Award expiration period from grant date					10 years
Employee stock ownership, combined voting power of all stock					10.00%
Minimum exercise price as a percentage of the fair value per share					110.00%
Award expiration period, for excess voting power grants					5 years
Grant date fair value, percentage					100.00%
Shares reserved for future issuance (in shares)					56,855,000	41,562,000
Compensation cost not yet recognized					$ 494,700,000
Weighted average remaining vesting period					3 years
Options assumed in acquisition (in shares)						63,000	4,579,000
Price per share (usd per share)									$ 82.00
Mandiant, Inc.
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost not yet recognized		$ 119,500,000
Options assumed in acquisition (in shares)				4,600,000
Options assumed in acquisition, vested (in shares)				2,100,000			2,100,000
Options assumed in acquisition, unvested (in shares)				2,500,000			2,500,000
Shares issued for acquisition (in shares)		16,123,011
Share price (usd per share)		$ 5.22
nPulse Technologies
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
General vesting period			3 years 6 months
Shares issued for acquisition (in shares)			295,681
Share price (usd per share)			$ 26.44
nPulse Technologies | Former shareholders
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued for acquisition (in shares)			54,319
nPulse Technologies | Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued for acquisition (in shares)			241,362
ESPP shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for future issuance (in shares)					3,200,000	2,700,000
Acquisition price at lower of fair market value, percentage					85.00%
Purchase period					12 months
Maximum employee payroll deduction, percentage					15.00%
Employee maximum number of shares per purchase period					3,000
Employee maximum purchase value of stock per year					$ 25,000
Common stock, percentage outstanding					1.00%
Shares outstanding threshold (in shares)					3,700,000
Performance shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued (in shares)					5,300,000	1,700,000	2,100,000
Restricted stock | Mandiant, Inc.
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average remaining vesting period				2 years
Shares issued for acquisition (in shares)				797,698
Price per share (usd per share)				$ 43.69			$ 43.69
Restricted stock | nPulse Technologies
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period					135,399
Restricted stock awards vested
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued (in shares)					16,876,000	6,734,000	1,949,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period					2,783,000	1,482,000	2,115,000
2013 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for future issuance (in shares)					7,178,860	13,314,131
Common stock available for future grants (in shares)								8,082,165
Minimum | 2013 Plan | Employee stock option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date fair value, percentage					100.00%
Subsequent Event | ESPP shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional shares authorized (in shares)	1,616,433