Goodwill and Other Intangible Assets (Prior Year Acquisitions) (Westower) (Narrative) (Details) - USD ($) $ in Millions		3 Months Ended			12 Months Ended
	Oct. 01, 2014	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Communications [Member]
Business Combinations [Line Items]
Business combinations, acquisition integration costs (in dollars)		$ 1.2	$ 7.8	$ 8.8		$ 17.8	$ 5.3
Communications [Member] | General and Administrative Expenses [Member]
Business Combinations [Line Items]
Business combinations, acquisition integration costs (in dollars)						17.8	5.3
WesTower [Member]
Business Combinations [Line Items]
Business combinations, effective date					Oct. 01, 2014
Business combinations, percentage of voting interests acquired					100.00%
Business combinations, name of acquired entity					WesTower Communications Inc. (“WesTower”)
Business combinations, description of acquired entity					a telecommunications services firm focused on communications infrastructure for wireless networks throughout the Eastern, Central and Western United States
Business combinations, payments in cash (in dollars)	$ 198.0
WesTower [Member] | Communications [Member] | General and Administrative Expenses [Member]
Business Combinations [Line Items]
Business combinations, acquisition integration costs (in dollars)						$ 9.3	$ 5.0