Investment in CyrusOne - Schedule of Related Party Transactions (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Balance Sheet Related Disclosures [Abstract]
Dividends receivable	$ 2.7	$ 9.0
CyrusOne [Member]
Revenue:
Services provided to CyrusOne	0.3	0.3
Operating costs and expenses:
Charges for services provided by CyrusOne	2.6	2.5
Administrative services provided to CyrusOne	(0.1)	(0.1)
Total operating costs and expenses	2.5	$ 2.4
Balance Sheet Related Disclosures [Abstract]
Accounts receivable	0.1		$ 0.1
Dividends receivable	2.7		2.1
Receivable from CyrusOne	2.8		2.2
Payable to CyrusOne	$ 1.4		$ 1.5