Supplemental Guarantor Information CBT Condensed Consolidating Balance Sheets (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	$ 9.7	$ 7.4	$ 57.9	$ 4.6
Other Assets, Current	3.9	2.2
Assets, Current	229.9	200.4
Property, plant and equipment, net	1,085.5	975.5
Investment in CyrusOne	128.0	55.5
Goodwill	14.3	14.3
Other Assets, Noncurrent	18.8	17.8
Assets	1,541.0	1,446.4
Current portion of long-term debt	7.5	13.8
Accounts payable	105.9	128.9
Other Liabilities, Current	31.9	25.0
Disposal Group, Including Discontinued Operation, Other Liabilities, Current	0.0	5.4
Liabilities, Current	232.9	259.2
Long-term Debt and Capital Lease Obligations	1,199.1	1,223.8
Other Liabilities, Noncurrent	33.0	36.6
Liabilities	1,662.7	1,744.6
Stockholders' Equity Attributable to Parent	(121.7)	(298.2)	(648.5)	(676.7)
Liabilities and Equity	1,541.0	1,446.4
Notes guaranteed by parent [Member]
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	9.7	7.4	57.9	4.6
Receivables, Net, Current	178.6	157.1
Other Assets, Current	41.6	35.9
Assets, Current	229.9	200.4
Property, plant and equipment, net	1,085.5	975.5
Investment in CyrusOne	128.0	55.5
Goodwill	14.3	14.3
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	0.0	0.0
Other Assets, Noncurrent	83.3	200.7
Assets	1,541.0	1,446.4
Current portion of long-term debt	7.5	13.8
Accounts payable	105.9	128.9
Other Liabilities, Current	119.5	111.1
Disposal Group, Including Discontinued Operation, Other Liabilities, Current	0.0	5.4
Liabilities, Current	232.9	259.2
Long-term Debt and Capital Lease Obligations	1,199.1	1,223.8
Other Liabilities, Noncurrent	230.7	261.6
Due to Related Parties, Noncurrent	0.0	0.0
Liabilities	1,662.7	1,744.6
Stockholders' Equity Attributable to Parent	(121.7)	(298.2)
Liabilities and Equity	1,541.0	1,446.4
Notes guaranteed by parent [Member] | Consolidation, Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	0.0	0.0	0.0	0.0
Receivables, Net, Current	0.0	0.0
Other Assets, Current	0.0	0.0
Assets, Current	0.0	0.0
Property, plant and equipment, net	0.0	0.0
Investment in CyrusOne	0.0	0.0
Goodwill	0.0	0.0
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	(1,731.2)	(1,555.7)
Other Assets, Noncurrent	(144.8)	(146.3)
Assets	(1,876.0)	(1,702.0)
Current portion of long-term debt	0.0	0.0
Accounts payable	0.0	0.0
Other Liabilities, Current	0.0	0.0
Disposal Group, Including Discontinued Operation, Other Liabilities, Current	0.0	0.0
Liabilities, Current	0.0	0.0
Long-term Debt and Capital Lease Obligations	0.0	0.0
Other Liabilities, Noncurrent	(144.8)	(146.2)
Due to Related Parties, Noncurrent	(89.1)	(54.7)
Liabilities	(233.9)	(200.9)
Stockholders' Equity Attributable to Parent	(1,642.1)	(1,501.1)
Liabilities and Equity	(1,876.0)	(1,702.0)
Notes guaranteed by parent [Member] | Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	7.8	4.6	56.2	2.1
Receivables, Net, Current	17.8	0.7
Other Assets, Current	1.1	1.6
Assets, Current	26.7	6.9
Property, plant and equipment, net	0.3	0.3
Investment in CyrusOne	0.0	0.0
Goodwill	0.0	0.0
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	816.7	844.6
Other Assets, Noncurrent	179.1	207.2
Assets	1,022.8	1,059.0
Current portion of long-term debt	0.0	5.4
Accounts payable	0.7	0.7
Other Liabilities, Current	42.9	41.6
Disposal Group, Including Discontinued Operation, Other Liabilities, Current	0.0	0.0
Liabilities, Current	43.6	47.7
Long-term Debt and Capital Lease Obligations	960.3	1,018.6
Other Liabilities, Noncurrent	207.9	235.5
Due to Related Parties, Noncurrent	0.0	54.7
Liabilities	1,211.8	1,356.5
Stockholders' Equity Attributable to Parent	(189.0)	(297.5)
Liabilities and Equity	1,022.8	1,059.0
Notes guaranteed by parent [Member] | Cincinnati Bell Telephone Company [Member]
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	1.4	1.0	1.0	1.8
Receivables, Net, Current	0.0	0.0
Other Assets, Current	22.3	20.2
Assets, Current	23.7	21.2
Property, plant and equipment, net	1,029.6	921.5
Investment in CyrusOne	0.0	0.0
Goodwill	2.2	2.2
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	0.0	63.9
Other Assets, Noncurrent	1.6	3.0
Assets	1,057.1	1,011.8
Current portion of long-term debt	5.0	5.0
Accounts payable	71.4	84.8
Other Liabilities, Current	53.9	45.3
Disposal Group, Including Discontinued Operation, Other Liabilities, Current	0.0	0.0
Liabilities, Current	130.3	135.1
Long-term Debt and Capital Lease Obligations	98.2	134.3
Other Liabilities, Noncurrent	166.8	168.3
Due to Related Parties, Noncurrent	89.1	0.0
Liabilities	484.4	437.7
Stockholders' Equity Attributable to Parent	572.7	574.1
Liabilities and Equity	1,057.1	1,011.8
Notes guaranteed by parent [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	0.5	1.8	$ 0.7	$ 0.7
Receivables, Net, Current	160.8	156.4
Other Assets, Current	18.2	14.1
Assets, Current	179.5	172.3
Property, plant and equipment, net	55.6	53.7
Investment in CyrusOne	128.0	55.5
Goodwill	12.1	12.1
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	914.5	647.2
Other Assets, Noncurrent	47.4	136.8
Assets	1,337.1	1,077.6
Current portion of long-term debt	2.5	3.4
Accounts payable	33.8	43.4
Other Liabilities, Current	22.7	24.2
Disposal Group, Including Discontinued Operation, Other Liabilities, Current	0.0	5.4
Liabilities, Current	59.0	76.4
Long-term Debt and Capital Lease Obligations	140.6	70.9
Other Liabilities, Noncurrent	0.8	4.0
Due to Related Parties, Noncurrent	0.0	0.0
Liabilities	200.4	151.3
Stockholders' Equity Attributable to Parent	1,136.7	926.3
Liabilities and Equity	$ 1,337.1	$ 1,077.6