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Employee Benefits And Stock-Based Compensation (Stock Based Compensation to Modifications) (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Closing price of Verisign's stock	$ 192.68
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 172.87	$ 112.74	$ 83.91
Income Tax Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Income tax benefit on stock-based compensation	$ 11.7	$ 12.3	$ 12.5
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation cost	$ 71.2
Weighted-average period of recognition for unrecognized compensation cost (in years)	2 years 6 months
Aggregate intrinsic value of unvested RSUs	$ 168.9
Fair values of vested RSUs	$ 124.1	$ 107.2	$ 70.9
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units with performance condition	300,000
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units with performance condition	0
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units with performance condition	600,000