Supplemental Guarantor Information - Condensed Consolidating Statements of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Condensed Consolidating Statements of Cash Flows
Cash flows provided by (used in) operating activities			$ 141.7	$ 94.7
Capital expenditures	$ (67.2)	$ (73.2)	(188.8)	(205.7)
Increase in restricted cash			(90.7)	0.0
Dividends received from CyrusOne			6.2	19.5
Proceeds from sale of CyrusOne			181.2	596.3
Proceeds from sale of assets			0.0	0.6
Other investing activities			(0.8)	(0.2)
Net cash (used in) provided by investing activities			(92.9)	410.5
Proceeds from issuance of long-term debt			425.0	0.0
Net (decrease) increase in corporate credit and receivables facilities with initial maturities less than 90 days			5.9	(19.2)
Repayment of debt			(461.0)	(509.8)
Debt issuance costs			(8.4)	(0.4)
Common stock repurchase			(4.8)	0.0
Other financing activities			3.4	(0.5)
Cash flows provided by (used in) financing activities			(47.7)	(537.7)
Increase (decrease) in cash and cash equivalents			1.1	(32.5)
Cash and cash equivalents at beginning of period			7.4	57.9
Cash and cash equivalents at end of period	8.5	25.4	8.5	25.4
Notes guaranteed by parent [Member]
Condensed Consolidating Statements of Cash Flows
Cash flows provided by (used in) operating activities			141.7	94.7
Capital expenditures			(188.8)	(205.7)
Increase in restricted cash			(90.7)
Dividends received from CyrusOne			6.2	19.5
Proceeds from sale of CyrusOne			181.2	596.3
Proceeds from sale of assets				0.6
Distributions received from subsidiaries			0.0	0.0
Funding between parent and subsidiaries, net			0.0	0.0
Other investing activities			(0.8)	(0.2)
Net cash (used in) provided by investing activities			(92.9)	410.5
Funding between parent and subsidiaries, net			0.0	0.0
Distributions paid to Parent			0.0	0.0
Proceeds from issuance of long-term debt			425.0
Net (decrease) increase in corporate credit and receivables facilities with initial maturities less than 90 days			5.9	(19.2)
Repayment of debt			(461.0)	(509.8)
Debt issuance costs			(8.4)	(0.4)
Common stock repurchase			(4.8)
Other financing activities			(4.4)	(8.3)
Cash flows provided by (used in) financing activities			(47.7)	(537.7)
Increase (decrease) in cash and cash equivalents			1.1	(32.5)
Cash and cash equivalents at beginning of period			7.4	57.9
Cash and cash equivalents at end of period	8.5	25.4	8.5	25.4
Notes guaranteed by parent [Member] | Consolidation, Eliminations [Member]
Condensed Consolidating Statements of Cash Flows
Cash flows provided by (used in) operating activities			0.0	0.0
Capital expenditures			0.0	0.0
Increase in restricted cash			0.0
Dividends received from CyrusOne			0.0	0.0
Proceeds from sale of CyrusOne			0.0	0.0
Proceeds from sale of assets				0.0
Distributions received from subsidiaries			(9.0)	(8.7)
Funding between parent and subsidiaries, net			62.4	499.4
Other investing activities			0.0	0.0
Net cash (used in) provided by investing activities			53.4	490.7
Funding between parent and subsidiaries, net			(62.4)	(499.4)
Distributions paid to Parent			9.0	8.7
Proceeds from issuance of long-term debt			0.0
Net (decrease) increase in corporate credit and receivables facilities with initial maturities less than 90 days			0.0	0.0
Repayment of debt			0.0	0.0
Debt issuance costs			0.0	0.0
Common stock repurchase			0.0
Other financing activities			0.0	0.0
Cash flows provided by (used in) financing activities			(53.4)	(490.7)
Increase (decrease) in cash and cash equivalents			0.0	0.0
Cash and cash equivalents at beginning of period			0.0	0.0
Cash and cash equivalents at end of period	0.0	0.0	0.0	0.0
Notes guaranteed by parent [Member] | Parent Company [Member]
Condensed Consolidating Statements of Cash Flows
Cash flows provided by (used in) operating activities			(41.9)	(13.5)
Capital expenditures			(0.2)	(0.1)
Increase in restricted cash			(90.7)
Dividends received from CyrusOne			0.0	0.0
Proceeds from sale of CyrusOne			0.0	0.0
Proceeds from sale of assets				0.0
Distributions received from subsidiaries			9.0	8.7
Funding between parent and subsidiaries, net			135.0	0.0
Other investing activities			(0.8)	(0.2)
Net cash (used in) provided by investing activities			52.3	8.4
Funding between parent and subsidiaries, net			0.0	482.9
Distributions paid to Parent			0.0	0.0
Proceeds from issuance of long-term debt			425.0
Net (decrease) increase in corporate credit and receivables facilities with initial maturities less than 90 days			0.0	0.0
Repayment of debt			(415.9)	(503.4)
Debt issuance costs			(8.1)	(0.2)
Common stock repurchase			(4.8)
Other financing activities			(4.4)	(8.3)
Cash flows provided by (used in) financing activities			(8.2)	(29.0)
Increase (decrease) in cash and cash equivalents			2.2	(34.1)
Cash and cash equivalents at beginning of period			4.6	56.2
Cash and cash equivalents at end of period	6.8	22.1	6.8	22.1
Notes guaranteed by parent [Member] | Cincinnati Bell Telephone Company [Member]
Condensed Consolidating Statements of Cash Flows
Cash flows provided by (used in) operating activities			145.3	162.2
Capital expenditures			(169.6)	(187.4)
Increase in restricted cash			0.0
Dividends received from CyrusOne			0.0	0.0
Proceeds from sale of CyrusOne			0.0	0.0
Proceeds from sale of assets				0.1
Distributions received from subsidiaries			0.0	0.0
Funding between parent and subsidiaries, net			0.0	29.3
Other investing activities			0.0	0.0
Net cash (used in) provided by investing activities			(169.6)	(158.0)
Funding between parent and subsidiaries, net			66.6	0.0
Distributions paid to Parent			0.0	0.0
Proceeds from issuance of long-term debt			0.0
Net (decrease) increase in corporate credit and receivables facilities with initial maturities less than 90 days			0.0	0.0
Repayment of debt			(42.3)	(3.7)
Debt issuance costs			0.0	0.0
Common stock repurchase			0.0
Other financing activities			0.0	0.0
Cash flows provided by (used in) financing activities			24.3	(3.7)
Increase (decrease) in cash and cash equivalents			0.0	0.5
Cash and cash equivalents at beginning of period			1.0	1.0
Cash and cash equivalents at end of period	1.0	1.5	1.0	1.5
Notes guaranteed by parent [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Consolidating Statements of Cash Flows
Cash flows provided by (used in) operating activities			38.3	(54.0)
Capital expenditures			(19.0)	(18.2)
Increase in restricted cash			0.0
Dividends received from CyrusOne			6.2	19.5
Proceeds from sale of CyrusOne			181.2	596.3
Proceeds from sale of assets				0.5
Distributions received from subsidiaries			0.0	0.0
Funding between parent and subsidiaries, net			(197.4)	(528.7)
Other investing activities			0.0	0.0
Net cash (used in) provided by investing activities			(29.0)	69.4
Funding between parent and subsidiaries, net			(4.2)	16.5
Distributions paid to Parent			(9.0)	(8.7)
Proceeds from issuance of long-term debt			0.0
Net (decrease) increase in corporate credit and receivables facilities with initial maturities less than 90 days			5.9	(19.2)
Repayment of debt			(2.8)	(2.7)
Debt issuance costs			(0.3)	(0.2)
Common stock repurchase			0.0
Other financing activities			0.0	0.0
Cash flows provided by (used in) financing activities			(10.4)	(14.3)
Increase (decrease) in cash and cash equivalents			(1.1)	1.1
Cash and cash equivalents at beginning of period			1.8	0.7
Cash and cash equivalents at end of period	0.7	1.8	0.7	1.8
Notes guaranteed by subsidiaries [Member]
Condensed Consolidating Statements of Cash Flows
Cash flows provided by (used in) operating activities			141.7	94.7
Capital expenditures			(188.8)	(205.7)
Increase in restricted cash			(90.7)
Dividends received from CyrusOne			6.2	19.5
Proceeds from sale of CyrusOne			181.2	596.3
Proceeds from sale of assets				0.6
Distributions received from subsidiaries			0.0	0.0
Funding between parent and subsidiaries, net			0.0	0.0
Other investing activities			(0.8)	(0.2)
Net cash (used in) provided by investing activities			(92.9)	410.5
Funding between parent and subsidiaries, net			0.0	0.0
Distributions paid to Parent			0.0	0.0
Proceeds from issuance of long-term debt			425.0
Net (decrease) increase in corporate credit and receivables facilities with initial maturities less than 90 days			5.9	(19.2)
Repayment of debt			(461.0)	(509.8)
Debt issuance costs			(8.4)	(0.4)
Common stock repurchase			(4.8)
Other financing activities			(4.4)	(8.3)
Cash flows provided by (used in) financing activities			(47.7)	(537.7)
Increase (decrease) in cash and cash equivalents			1.1	(32.5)
Cash and cash equivalents at beginning of period			7.4	57.9
Cash and cash equivalents at end of period	8.5	25.4	8.5	25.4
Notes guaranteed by subsidiaries [Member] | Consolidation, Eliminations [Member]
Condensed Consolidating Statements of Cash Flows
Cash flows provided by (used in) operating activities			0.0	0.0
Capital expenditures			0.0	0.0
Increase in restricted cash			0.0
Dividends received from CyrusOne			0.0	0.0
Proceeds from sale of CyrusOne			0.0	0.0
Proceeds from sale of assets				0.0
Distributions received from subsidiaries			(9.0)	(8.7)
Funding between parent and subsidiaries, net			48.3	501.8
Other investing activities			0.0	0.0
Net cash (used in) provided by investing activities			39.3	493.1
Funding between parent and subsidiaries, net			(48.3)	(501.8)
Distributions paid to Parent			9.0	8.7
Proceeds from issuance of long-term debt			0.0
Net (decrease) increase in corporate credit and receivables facilities with initial maturities less than 90 days			0.0	0.0
Repayment of debt			0.0	0.0
Debt issuance costs			0.0	0.0
Common stock repurchase			0.0
Other financing activities			0.0	0.0
Cash flows provided by (used in) financing activities			(39.3)	(493.1)
Increase (decrease) in cash and cash equivalents			0.0	0.0
Cash and cash equivalents at beginning of period			0.0	0.0
Cash and cash equivalents at end of period	0.0	0.0	0.0	0.0
Notes guaranteed by subsidiaries [Member] | Parent Company [Member]
Condensed Consolidating Statements of Cash Flows
Cash flows provided by (used in) operating activities			(41.9)	(13.5)
Capital expenditures			(0.2)	(0.1)
Increase in restricted cash			(90.7)
Dividends received from CyrusOne			0.0	0.0
Proceeds from sale of CyrusOne			0.0	0.0
Proceeds from sale of assets				0.0
Distributions received from subsidiaries			9.0	8.7
Funding between parent and subsidiaries, net			135.0	0.0
Other investing activities			(0.8)	(0.2)
Net cash (used in) provided by investing activities			52.3	8.4
Funding between parent and subsidiaries, net			0.0	482.9
Distributions paid to Parent			0.0	0.0
Proceeds from issuance of long-term debt			425.0
Net (decrease) increase in corporate credit and receivables facilities with initial maturities less than 90 days			0.0	0.0
Repayment of debt			(415.9)	(503.4)
Debt issuance costs			(8.1)	(0.2)
Common stock repurchase			(4.8)
Other financing activities			(4.4)	(8.3)
Cash flows provided by (used in) financing activities			(8.2)	(29.0)
Increase (decrease) in cash and cash equivalents			2.2	(34.1)
Cash and cash equivalents at beginning of period			4.6	56.2
Cash and cash equivalents at end of period	6.8	22.1	6.8	22.1
Notes guaranteed by subsidiaries [Member] | Guarantor Subsidiaries [Member]
Condensed Consolidating Statements of Cash Flows
Cash flows provided by (used in) operating activities			17.5	(35.0)
Capital expenditures			(19.0)	(18.2)
Increase in restricted cash			0.0
Dividends received from CyrusOne			6.2	19.5
Proceeds from sale of CyrusOne			181.2	596.3
Proceeds from sale of assets				0.5
Distributions received from subsidiaries			0.0	0.0
Funding between parent and subsidiaries, net			(183.3)	(560.3)
Other investing activities			0.0	0.0
Net cash (used in) provided by investing activities			(14.9)	37.8
Funding between parent and subsidiaries, net			0.0	0.0
Distributions paid to Parent			0.0	0.0
Proceeds from issuance of long-term debt			0.0
Net (decrease) increase in corporate credit and receivables facilities with initial maturities less than 90 days			0.0	0.0
Repayment of debt			(2.8)	(2.7)
Debt issuance costs			0.0	0.0
Common stock repurchase			0.0
Other financing activities			0.0	0.0
Cash flows provided by (used in) financing activities			(2.8)	(2.7)
Increase (decrease) in cash and cash equivalents			(0.2)	0.1
Cash and cash equivalents at beginning of period			0.4	0.2
Cash and cash equivalents at end of period	0.2	0.3	0.2	0.3
Notes guaranteed by subsidiaries [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Consolidating Statements of Cash Flows
Cash flows provided by (used in) operating activities			166.1	143.2
Capital expenditures			(169.6)	(187.4)
Increase in restricted cash			0.0
Dividends received from CyrusOne			0.0	0.0
Proceeds from sale of CyrusOne			0.0	0.0
Proceeds from sale of assets				0.1
Distributions received from subsidiaries			0.0	0.0
Funding between parent and subsidiaries, net			0.0	58.5
Other investing activities			0.0	0.0
Net cash (used in) provided by investing activities			(169.6)	(128.8)
Funding between parent and subsidiaries, net			48.3	18.9
Distributions paid to Parent			(9.0)	(8.7)
Proceeds from issuance of long-term debt			0.0
Net (decrease) increase in corporate credit and receivables facilities with initial maturities less than 90 days			5.9	(19.2)
Repayment of debt			(42.3)	(3.7)
Debt issuance costs			(0.3)	(0.2)
Common stock repurchase			0.0
Other financing activities			0.0	0.0
Cash flows provided by (used in) financing activities			2.6	(12.9)
Increase (decrease) in cash and cash equivalents			(0.9)	1.5
Cash and cash equivalents at beginning of period			2.4	1.5
Cash and cash equivalents at end of period	$ 1.5	$ 3.0	$ 1.5	$ 3.0