Repurchases of ARRIS Shares (Parentheticals) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2018	Mar. 31, 2018	Jun. 30, 2018
Equity, Class of Treasury Stock [Line Items]
Shares repurchased	8,400,000	1,000,000	4,000,000
Shares repurchased, value	$ 212.2	$ 25.0	$ 99.9
Repurchased to satisfy tax withholding obligations on vesting shares
Equity, Class of Treasury Stock [Line Items]
Shares subject to equity awards cancelled for cash to satisfy minimum tax withholding obligations	234,872
Stock Repurchased Pending Settlement
Equity, Class of Treasury Stock [Line Items]
Shares repurchased	210,654
Shares repurchased, value	$ 5.5