Other Financial Information - Deferred Revenue (Details) - USD ($) $ in Millions	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Reported as:
Current	$ 888.2	$ 818.6	$ 1,030.3
Long-term	368.7	$ 384.4	509.0
Deferred revenue	1,256.9		1,539.3
Undelivered product commitments and other product deferrals
Deferred product revenue:
Deferred gross product revenue	166.4		312.6
Distributor inventory and other sell-through items
Deferred product revenue:
Deferred gross product revenue	0.0		68.1
Product
Deferred product revenue:
Deferred gross product revenue	166.4		380.7
Deferred cost of product revenue	(7.6)		(46.5)
Reported as:
Deferred revenue	158.8		334.2
Service
Reported as:
Deferred revenue	$ 1,098.1		$ 1,205.1