Net Income per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Numerator:
Net income (loss)	$ 197.8	$ 197.7	$ 158.0	$ 80.2	$ (769.6)	$ 103.6	$ 221.1	$ 110.6	$ 633.7	$ (334.3)	$ 439.8
Denominator:
Weighted-average shares used to compute basic net income (loss) per share									390.6	457.4	501.8
Dilutive effect of employee stock awards									8.8	0.0	8.5
Weighted-average shares used to compute diluted net income (loss) per share									399.4	457.4	510.3
Net income (loss) per share attributable to Juniper Networks common stockholders:
Basic (in dollars per share)	$ 0.52	$ 0.52	$ 0.41	$ 0.20	$ (1.81)	$ 0.23	$ 0.47	$ 0.23	$ 1.62	$ (0.73)	$ 0.88
Diluted (in dollars per share)	$ 0.51	$ 0.51	$ 0.40	$ 0.19	$ (1.81)	$ 0.23	$ 0.46	$ 0.22	$ 1.59	$ (0.73)	$ 0.86
Net Income (Loss) per Share Textuals
Anti-dilutive shares excluded from computation of diluted earnings per share									3.4	20.8	13.2