Supplemental Guarantor Information HY (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Condensed Consolidating Statements of Operations and Comprehensive Income (Loss) [Abstract]
Revenue	$ 308.3	$ 327.5	$ 319.9	$ 322.5	$ 308.4	$ 310.8	$ 312.0	$ 325.7	$ 1,278.2	$ 1,256.9	$ 1,473.9
Operating costs and expenses									1,162.4	1,093.1	1,203.8
Operating income (loss)	7.3	16.0	35.6	56.9	40.1	57.7	46.8	19.2	115.8	163.8	270.1
Interest expense (income), net									148.7	182.0	218.9
Other expense (income), net									0.3	(1.3)	1.7
Income (loss) before equity in earnings of subsidiaries and income taxes									133.0	(57.2)	35.9
Income tax expense (benefit)									57.4	(2.5)	24.7
Net income (loss)	(18.3)	(27.3)	114.2	7.0	(28.1)	9.3	0.8	(36.7)	75.6	(54.7)	11.2
Other comprehensive income (loss)									(40.6)	76.4	(0.8)
Total comprehensive income (loss)									35.0	21.7	10.4
Preferred stock dividends									10.4	10.4	10.4
Net income (loss) applicable to common shareowners									65.2	(65.1)	0.8
Condensed Consolidating Balance Sheets [Abstract]
Cash and cash equivalents	57.9				4.6				57.9	4.6	23.6
Other current assets	2.0				1.6				2.0	1.6
Total current assets	336.6				251.1				336.6	251.1
Property, plant and equipment, net	859.5				902.8				859.5	902.8
Investment in CyrusOne	273.6				471.0				273.6	471.0
Other noncurrent assets	33.9				36.6				33.9	36.6
Total assets	1,819.7				2,107.3				1,819.7	2,107.3
Current portion of long-term debt	13.2				12.6				13.2	12.6
Accounts payable	135.6				89.4				135.6	89.4
Deferred gain in wireless spectrum licenses	112.6				0				112.6	0
Other current liabilities	46.3				36.8				46.3	36.8
Total current liabilities	409.8				254.3				409.8	254.3
Long-term debt, less current portion	1,771.0				2,252.6				1,771.0	2,252.6
Other noncurrent liabilities	47.3				74.4				47.3	74.4
Total liabilities	2,468.2				2,784.0				2,468.2	2,784.0
Shareowners' (deficit) equity	(648.5)				(676.7)				(648.5)	(676.7)	(698.2)	(715.2)
Total liabilities and shareowners' equity (deficit)	1,819.7				2,107.3				1,819.7	2,107.3
Condensed Consolidating Statements of Cash Flows [Abstract]
Cash flows (used in) provided by operating activities									175.2	78.8	212.7
Capital expenditures									(182.3)	(196.9)	(367.2)
Proceeds from sale of CyrusOne equity method investment			355.9						355.9	0	0
Dividends received from CyrusOne									28.4	21.3	0
Proceeds from sale of assets									2.0	2.0	1.6
Cash divested from deconsolidation of CyrusOne									0	(12.2)	0
Other investing activities									(5.8)	0	0
Cash flows provided by (used in) investing activities									392.6	(185.4)	(371.8)
Proceeds from issuance of long-term debt									0	536.0	525.0
Debt issuance costs									(0.9)	(6.7)	(20.9)
Net increase in corporate credit and receivables facilities with initial maturities less than 90 days									(127.0)	94.2	52.0
Repayment of debt									(376.5)	(530.8)	(442.4)
Common stock issuance costs									0	0	(5.7)
Common stock repurchase									0	0	(0.3)
Proceeds from exercise of options and warrants									1.3	7.1	12.1
Other financing activities									(1.1)	(2.3)	(2.8)
Cash flows provided by (used in) financing activities									(514.5)	87.6	109.0
(Decrease) increase in cash and cash equivalents									53.3	(19.0)	(50.1)
Cash and cash equivalents at beginning of year				4.6				23.6	4.6	23.6	73.7
Cash and cash equivalents at end of year	57.9				4.6				57.9	4.6	23.6
Notes guaranteed by subsidiaries [Member]
Condensed Consolidating Statements of Operations and Comprehensive Income (Loss) [Abstract]
Revenue									1,278.2	1,256.9	1,473.9
Operating costs and expenses									1,162.4	1,093.1	1,203.8
Operating income (loss)									115.8	163.8	270.1
Interest expense (income), net									148.7	182.0	218.9
Other expense (income), net									(165.9)	39.0	15.3
Income (loss) before equity in earnings of subsidiaries and income taxes									133.0	(57.2)	35.9
Income tax expense (benefit)									57.4	(2.5)	24.7
Equity in earnings of subsidiaries, net of tax									0	0	0
Net income (loss)									75.6	(54.7)	11.2
Other comprehensive income (loss)									(40.6)	76.4	(0.8)
Total comprehensive income (loss)									35.0	21.7	10.4
Preferred stock dividends									10.4	10.4	10.4
Net income (loss) applicable to common shareowners									65.2	(65.1)	0.8
Condensed Consolidating Balance Sheets [Abstract]
Cash and cash equivalents	57.9				4.6				57.9	4.6	23.6
Receivables, net	167.5				154.8				167.5	154.8
Other current assets	111.2				91.7				111.2	91.7
Total current assets	336.6				251.1				336.6	251.1
Property, plant and equipment, net	859.5				902.8				859.5	902.8
Investment in CyrusOne	273.6				471.0				273.6	471.0
Goodwill and intangibles, net	15.4				106.1				15.4	106.1
Investments in and advances to subsidiaries	0				0				0	0
Other noncurrent assets	334.6				376.3				334.6	376.3
Total assets	1,819.7				2,107.3				1,819.7	2,107.3
Current portion of long-term debt	13.2				12.6				13.2	12.6
Accounts payable	136.0				89.9				136.0	89.9
Deferred gain in wireless spectrum licenses	112.6								112.6
Other current liabilities	148.0				151.8				148.0	151.8
Total current liabilities	409.8				254.3				409.8	254.3
Long-term debt, less current portion	1,771.0				2,252.6				1,771.0	2,252.6
Other noncurrent liabilities	287.4				277.1				287.4	277.1
Intercompany payables	0				0				0	0
Total liabilities	2,468.2				2,784.0				2,468.2	2,784.0
Shareowners' (deficit) equity	(648.5)				(676.7)				(648.5)	(676.7)
Total liabilities and shareowners' equity (deficit)	1,819.7				2,107.3				1,819.7	2,107.3
Condensed Consolidating Statements of Cash Flows [Abstract]
Cash flows (used in) provided by operating activities									175.2	78.8	212.7
Capital expenditures									(182.3)	(196.9)	(367.2)
Proceeds from sale of CyrusOne equity method investment									355.9
Dividends received from CyrusOne									28.4	21.3
Proceeds from sale of assets									196.4	2.0	1.6
Distributions received from subsidiaries									0
Funding between Parent and subsidiaries, net investing									0
Cash divested from deconsolidation of CyrusOne										(12.2)
Other investing activities									(5.8)	0.4	(6.2)
Cash flows provided by (used in) investing activities									392.6	(185.4)	(371.8)
Funding between Parent and subsidiaries, net financing									0
Distributions paid to Parent									0
Proceeds from issuance of long-term debt										536.0	525.0
Funding between Parent and subsidiaries, net										0	0
Debt issuance costs									(0.9)	(6.7)	(20.9)
Net increase in corporate credit and receivables facilities with initial maturities less than 90 days									(127.0)	94.2	52.0
Repayment of debt									(376.5)	(530.8)	(442.4)
Common stock issuance costs											(5.7)
Common stock repurchase											(0.3)
Proceeds from exercise of options and warrants									1.3	7.1	12.1
Other financing activities									(11.4)	(12.2)	(10.8)
Cash flows provided by (used in) financing activities									(514.5)	87.6	109.0
(Decrease) increase in cash and cash equivalents									53.3	(19.0)	(50.1)
Cash and cash equivalents at beginning of year				4.6				23.6	4.6	23.6	73.7
Cash and cash equivalents at end of year	57.9				4.6				57.9	4.6	23.6
Notes guaranteed by subsidiaries [Member] | Parent Company [Member]
Condensed Consolidating Statements of Operations and Comprehensive Income (Loss) [Abstract]
Revenue									0	0	0
Operating costs and expenses									19.9	55.4	33.9
Operating income (loss)									(19.9)	(55.4)	(33.9)
Interest expense (income), net									144.0	164.3	164.8
Other expense (income), net									17.6	28.2	11.5
Income (loss) before equity in earnings of subsidiaries and income taxes									(181.5)	(247.9)	(210.2)
Income tax expense (benefit)									(55.6)	(79.8)	(68.3)
Equity in earnings of subsidiaries, net of tax									201.5	113.4	153.1
Net income (loss)									75.6	(54.7)	11.2
Other comprehensive income (loss)									(40.5)	76.5	(0.8)
Total comprehensive income (loss)									35.1	21.8	10.4
Preferred stock dividends									10.4	10.4	10.4
Net income (loss) applicable to common shareowners									65.2	(65.1)	0.8
Condensed Consolidating Balance Sheets [Abstract]
Cash and cash equivalents	56.2				2.1				56.2	2.1	3.8
Receivables, net	2.6				2.6				2.6	2.6
Other current assets	4.7				4.4				4.7	4.4
Total current assets	63.5				9.1				63.5	9.1
Property, plant and equipment, net	0.2				0.1				0.2	0.1
Investment in CyrusOne	0				0				0	0
Goodwill and intangibles, net	0				0				0	0
Investments in and advances to subsidiaries	1,066.1				1,406.6				1,066.1	1,406.6
Other noncurrent assets	294.2				359.1				294.2	359.1
Total assets	1,424.0				1,774.9				1,424.0	1,774.9
Current portion of long-term debt	5.4				5.4				5.4	5.4
Accounts payable	1.0				1.5				1.0	1.5
Deferred gain in wireless spectrum licenses	0								0
Other current liabilities	52.3				67.7				52.3	67.7
Total current liabilities	58.7				74.6				58.7	74.6
Long-term debt, less current portion	1,526.1				1,916.1				1,526.1	1,916.1
Other noncurrent liabilities	254.1				214.5				254.1	214.5
Intercompany payables	233.4				246.4				233.4	246.4
Total liabilities	2,072.3				2,451.6				2,072.3	2,451.6
Shareowners' (deficit) equity	(648.3)				(676.7)				(648.3)	(676.7)
Total liabilities and shareowners' equity (deficit)	1,424.0				1,774.9				1,424.0	1,774.9
Condensed Consolidating Statements of Cash Flows [Abstract]
Cash flows (used in) provided by operating activities									(56.3)	(218.1)	(144.8)
Capital expenditures									(0.2)	0	0
Proceeds from sale of CyrusOne equity method investment									0
Dividends received from CyrusOne									0	0
Proceeds from sale of assets									0	0	0
Distributions received from subsidiaries									12.8
Funding between Parent and subsidiaries, net investing									0
Cash divested from deconsolidation of CyrusOne										0
Other investing activities									(0.3)	0	0
Cash flows provided by (used in) investing activities									12.3	0	0
Funding between Parent and subsidiaries, net financing									516.2
Distributions paid to Parent									0
Proceeds from issuance of long-term debt										536.0	0
Funding between Parent and subsidiaries, net										174.2	433.6
Debt issuance costs									(0.7)	(6.7)	(3.6)
Net increase in corporate credit and receivables facilities with initial maturities less than 90 days									(40.0)	40.0	0
Repayment of debt									(367.3)	(522.0)	(352.0)
Common stock issuance costs											0
Common stock repurchase											(0.3)
Proceeds from exercise of options and warrants									1.3	7.1	12.1
Other financing activities									(11.4)	(12.2)	(10.8)
Cash flows provided by (used in) financing activities									98.1	216.4	79.0
(Decrease) increase in cash and cash equivalents									54.1	(1.7)	(65.8)
Cash and cash equivalents at beginning of year				2.1				3.8	2.1	3.8	69.6
Cash and cash equivalents at end of year	56.2				2.1				56.2	2.1	3.8
Notes guaranteed by subsidiaries [Member] | Guarantor Subsidiaries [Member]
Condensed Consolidating Statements of Operations and Comprehensive Income (Loss) [Abstract]
Revenue									731.9	704.6	713.4
Operating costs and expenses									766.6	667.5	646.5
Operating income (loss)									(34.7)	37.1	66.9
Interest expense (income), net									7.8	14.9	7.8
Other expense (income), net									(171.2)	17.4	9.1
Income (loss) before equity in earnings of subsidiaries and income taxes									128.7	4.8	50.0
Income tax expense (benefit)									45.4	9.7	19.2
Equity in earnings of subsidiaries, net of tax									0	0.7	(11.8)
Net income (loss)									83.3	(4.2)	19.0
Other comprehensive income (loss)									(0.1)	0	0
Total comprehensive income (loss)									83.2	(4.2)	19.0
Preferred stock dividends									0	0	0
Net income (loss) applicable to common shareowners									83.3	(4.2)	19.0
Condensed Consolidating Balance Sheets [Abstract]
Cash and cash equivalents	0.2				0.3				0.2	0.3	0.3
Receivables, net	6.1				7.2				6.1	7.2
Other current assets	74.6				60.7				74.6	60.7
Total current assets	80.9				68.2				80.9	68.2
Property, plant and equipment, net	94.9				194.1				94.9	194.1
Investment in CyrusOne	273.6				471.0				273.6	471.0
Goodwill and intangibles, net	13.2				103.8				13.2	103.8
Investments in and advances to subsidiaries	387.8				(1.6)				387.8	(1.6)
Other noncurrent assets	191.6				179.9				191.6	179.9
Total assets	1,042.0				1,015.4				1,042.0	1,015.4
Current portion of long-term debt	3.9				3.0				3.9	3.0
Accounts payable	80.8				72.3				80.8	72.3
Deferred gain in wireless spectrum licenses	112.6								112.6
Other current liabilities	46.3				36.9				46.3	36.9
Total current liabilities	243.6				112.2				243.6	112.2
Long-term debt, less current portion	84.5				87.0				84.5	87.0
Other noncurrent liabilities	25.7				61.3				25.7	61.3
Intercompany payables	0				149.9				0	149.9
Total liabilities	353.8				410.4				353.8	410.4
Shareowners' (deficit) equity	688.2				605.0				688.2	605.0
Total liabilities and shareowners' equity (deficit)	1,042.0				1,015.4				1,042.0	1,015.4
Condensed Consolidating Statements of Cash Flows [Abstract]
Cash flows (used in) provided by operating activities									(1.4)	26.2	51.3
Capital expenditures									(29.6)	(36.1)	(30.2)
Proceeds from sale of CyrusOne equity method investment									355.9
Dividends received from CyrusOne									28.4	21.3
Proceeds from sale of assets									194.4	0	0
Distributions received from subsidiaries									0
Funding between Parent and subsidiaries, net investing									(539.3)
Cash divested from deconsolidation of CyrusOne										0
Other investing activities									(5.5)	0	0
Cash flows provided by (used in) investing activities									4.3	(14.8)	(30.2)
Funding between Parent and subsidiaries, net financing									0
Distributions paid to Parent									0
Proceeds from issuance of long-term debt										0	0
Funding between Parent and subsidiaries, net										(7.4)	(16.9)
Debt issuance costs									0	0	0
Net increase in corporate credit and receivables facilities with initial maturities less than 90 days									0	0	0
Repayment of debt									(3.0)	(4.0)	(4.6)
Common stock issuance costs											0
Common stock repurchase											0
Proceeds from exercise of options and warrants									0	0	0
Other financing activities									0	0	0
Cash flows provided by (used in) financing activities									(3.0)	(11.4)	(21.5)
(Decrease) increase in cash and cash equivalents									(0.1)	0	(0.4)
Cash and cash equivalents at beginning of year				0.3				0.3	0.3	0.3	0.7
Cash and cash equivalents at end of year	0.2				0.3				0.2	0.3	0.3
Notes guaranteed by subsidiaries [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Consolidating Statements of Operations and Comprehensive Income (Loss) [Abstract]
Revenue									601.5	608.6	822.7
Operating costs and expenses									431.1	426.5	585.6
Operating income (loss)									170.4	182.1	237.1
Interest expense (income), net									(3.1)	2.8	46.3
Other expense (income), net									(12.3)	(6.6)	(5.3)
Income (loss) before equity in earnings of subsidiaries and income taxes									185.8	185.9	196.1
Income tax expense (benefit)									67.6	67.6	73.8
Equity in earnings of subsidiaries, net of tax									0	0	0
Net income (loss)									118.2	118.3	122.3
Other comprehensive income (loss)									0	(0.1)	0
Total comprehensive income (loss)									118.2	118.2	122.3
Preferred stock dividends									0	0	0
Net income (loss) applicable to common shareowners									118.2	118.3	122.3
Condensed Consolidating Balance Sheets [Abstract]
Cash and cash equivalents	1.5				2.2				1.5	2.2	19.5
Receivables, net	158.8				145.0				158.8	145.0
Other current assets	33.1				27.3				33.1	27.3
Total current assets	193.4				174.5				193.4	174.5
Property, plant and equipment, net	764.4				708.6				764.4	708.6
Investment in CyrusOne	0				0				0	0
Goodwill and intangibles, net	2.2				2.3				2.2	2.3
Investments in and advances to subsidiaries	214.6				218.2				214.6	218.2
Other noncurrent assets	3.8				5.1				3.8	5.1
Total assets	1,178.4				1,108.7				1,178.4	1,108.7
Current portion of long-term debt	3.9				4.2				3.9	4.2
Accounts payable	54.2				16.1				54.2	16.1
Deferred gain in wireless spectrum licenses	0								0
Other current liabilities	49.3				47.1				49.3	47.1
Total current liabilities	107.4				67.4				107.4	67.4
Long-term debt, less current portion	160.4				249.5				160.4	249.5
Other noncurrent liabilities	164.0				169.9				164.0	169.9
Intercompany payables	131.9				33.2				131.9	33.2
Total liabilities	563.7				520.0				563.7	520.0
Shareowners' (deficit) equity	614.7				588.7				614.7	588.7
Total liabilities and shareowners' equity (deficit)	1,178.4				1,108.7				1,178.4	1,108.7
Condensed Consolidating Statements of Cash Flows [Abstract]
Cash flows (used in) provided by operating activities									232.9	270.7	306.2
Capital expenditures									(152.5)	(160.8)	(337.0)
Proceeds from sale of CyrusOne equity method investment									0
Dividends received from CyrusOne									0	0
Proceeds from sale of assets									2.0	2.0	1.6
Distributions received from subsidiaries									0
Funding between Parent and subsidiaries, net investing									(78.0)
Cash divested from deconsolidation of CyrusOne										(12.2)
Other investing activities									0	0.4	(6.2)
Cash flows provided by (used in) investing activities									(228.5)	(170.6)	(341.6)
Funding between Parent and subsidiaries, net financing									101.1
Distributions paid to Parent									(12.8)
Proceeds from issuance of long-term debt										0	525.0
Funding between Parent and subsidiaries, net										(166.8)	(416.7)
Debt issuance costs									(0.2)	0	(17.3)
Net increase in corporate credit and receivables facilities with initial maturities less than 90 days									(87.0)	54.2	52.0
Repayment of debt									(6.2)	(4.8)	(85.8)
Common stock issuance costs											(5.7)
Common stock repurchase											0
Proceeds from exercise of options and warrants									0	0	0
Other financing activities									0	0	0
Cash flows provided by (used in) financing activities									(5.1)	(117.4)	51.5
(Decrease) increase in cash and cash equivalents									(0.7)	(17.3)	16.1
Cash and cash equivalents at beginning of year				2.2				19.5	2.2	19.5	3.4
Cash and cash equivalents at end of year	1.5				2.2				1.5	2.2	19.5
Notes guaranteed by subsidiaries [Member] | Consolidation, Eliminations [Member]
Condensed Consolidating Statements of Operations and Comprehensive Income (Loss) [Abstract]
Revenue									(55.2)	(56.3)	(62.2)
Operating costs and expenses									(55.2)	(56.3)	(62.2)
Operating income (loss)									0	0	0
Interest expense (income), net									0	0	0
Other expense (income), net									0	0	0
Income (loss) before equity in earnings of subsidiaries and income taxes									0	0	0
Income tax expense (benefit)									0	0	0
Equity in earnings of subsidiaries, net of tax									(201.5)	(114.1)	(141.3)
Net income (loss)									(201.5)	(114.1)	(141.3)
Other comprehensive income (loss)									0	0	0
Total comprehensive income (loss)									(201.5)	(114.1)	(141.3)
Preferred stock dividends									0	0	0
Net income (loss) applicable to common shareowners									(201.5)	(114.1)	(141.3)
Condensed Consolidating Balance Sheets [Abstract]
Cash and cash equivalents	0				0				0	0	0
Receivables, net	0				0				0	0
Other current assets	(1.2)				(0.7)				(1.2)	(0.7)
Total current assets	(1.2)				(0.7)				(1.2)	(0.7)
Property, plant and equipment, net	0				0				0	0
Investment in CyrusOne	0				0				0	0
Goodwill and intangibles, net	0				0				0	0
Investments in and advances to subsidiaries	(1,668.5)				(1,623.2)				(1,668.5)	(1,623.2)
Other noncurrent assets	(155.0)				(167.8)				(155.0)	(167.8)
Total assets	(1,824.7)				(1,791.7)				(1,824.7)	(1,791.7)
Current portion of long-term debt	0				0				0	0
Accounts payable	0				0				0	0
Deferred gain in wireless spectrum licenses	0								0
Other current liabilities	0.1				0.1				0.1	0.1
Total current liabilities	0.1				0.1				0.1	0.1
Long-term debt, less current portion	0				0				0	0
Other noncurrent liabilities	(156.4)				(168.6)				(156.4)	(168.6)
Intercompany payables	(365.3)				(429.5)				(365.3)	(429.5)
Total liabilities	(521.6)				(598.0)				(521.6)	(598.0)
Shareowners' (deficit) equity	(1,303.1)				(1,193.7)				(1,303.1)	(1,193.7)
Total liabilities and shareowners' equity (deficit)	(1,824.7)				(1,791.7)				(1,824.7)	(1,791.7)
Condensed Consolidating Statements of Cash Flows [Abstract]
Cash flows (used in) provided by operating activities									0	0	0
Capital expenditures									0	0	0
Proceeds from sale of CyrusOne equity method investment									0
Dividends received from CyrusOne									0	0
Proceeds from sale of assets									0	0	0
Distributions received from subsidiaries									(12.8)
Funding between Parent and subsidiaries, net investing									617.3
Cash divested from deconsolidation of CyrusOne										0
Other investing activities									0	0	0
Cash flows provided by (used in) investing activities									604.5	0	0
Funding between Parent and subsidiaries, net financing									(617.3)
Distributions paid to Parent									12.8
Proceeds from issuance of long-term debt										0	0
Funding between Parent and subsidiaries, net										0	0
Debt issuance costs									0	0	0
Net increase in corporate credit and receivables facilities with initial maturities less than 90 days									0	0	0
Repayment of debt									0	0	0
Common stock issuance costs											0
Common stock repurchase											0
Proceeds from exercise of options and warrants									0	0	0
Other financing activities									0	0	0
Cash flows provided by (used in) financing activities									(604.5)	0	0
(Decrease) increase in cash and cash equivalents									0	0	0
Cash and cash equivalents at beginning of year				0				0	0	0	0
Cash and cash equivalents at end of year	$ 0				$ 0				$ 0	$ 0	$ 0