Consolidated Statements of Shareowners' Deficit - USD ($) shares in Millions, $ in Millions		3 Months Ended				12 Months Ended
		Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2016
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			$ (117.9)		$ (101.4)	$ (117.9)	$ (101.4)	$ (298.2)
Cumulative effect of adopting ASC Topic 606									$ 19.4
Net income (loss)		$ (30.0)	$ (8.3)	$ (11.9)	$ 60.6	(69.8)	40.0	103.0
Other comprehensive income (loss)						(1.8)	(51.2)	80.7
Reclassification adjustment to accumulated deficit for stranded other comprehensive income taxes arising from tax reform (a)							0.0
Shares issued under employee plans						0.2	0.5	3.6
Shares purchased under employee plans and other						(2.1)	(1.3)	(0.2)
Stock-based compensation						$ 5.6	$ 5.9	$ 5.1
Repurchase and retirement of shares						0.0	0.0	(0.2)
Repurchase and retirement of shares								$ (4.8)
Dividends on preferred stock						$ (10.4)	$ (10.4)	(10.4)
Stock consideration for acquisition of Hawaiian Telcom						7.7
Stock consideration for acquisition of Hawaiian Telcom						$ 121.2
Ending Balance		$ (75.0)		$ (117.9)		$ (75.0)	$ (117.9)	$ (101.4)
Preferred Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance			3.1		3.1	3.1	3.1	3.1
Beginning Balance			$ 129.4		$ 129.4	$ 129.4	$ 129.4	$ 129.4
Balance		3.1		3.1		3.1	3.1	3.1
Ending Balance		$ 129.4		$ 129.4		$ 129.4	$ 129.4	$ 129.4
Common Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance			42.2		42.1	42.2	42.1	42.0
Beginning Balance			$ 0.4		$ 0.4	$ 0.4	$ 0.4	$ 0.4
Shares issued under employee plans						0.3	0.1	0.3
Shares issued under employee plans						$ 0.0	$ 0.0	$ 0.0
Repurchase and retirement of shares								(0.2)
Repurchase and retirement of shares								$ 0.0
Stock consideration for acquisition of Hawaiian Telcom						7.7
Stock consideration for acquisition of Hawaiian Telcom						$ 0.1
Balance		50.2		42.2		50.2	42.2	42.1
Ending Balance		$ 0.5		$ 0.4		$ 0.5	$ 0.4	$ 0.4
Additional Paid-in Capital [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			2,565.6		2,570.9	2,565.6	2,570.9	2,577.7
Shares issued under employee plans						0.2	0.5	3.6
Shares purchased under employee plans and other						(2.1)	(1.3)	(0.3)
Stock-based compensation						5.6	5.9	5.1
Repurchase and retirement of shares								(4.8)
Dividends on preferred stock						(10.4)	(10.4)	(10.4)
Stock consideration for acquisition of Hawaiian Telcom						121.1
Ending Balance		2,680.0		2,565.6		2,680.0	2,565.6	2,570.9
Retained Earnings [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			(2,639.6)		(2,711.8)	(2,639.6)	(2,711.8)	(2,834.2)
Cumulative effect of adopting ASC Topic 606									$ 19.4
Net income (loss)						(69.8)	40.0	103.0
Reclassification adjustment to accumulated deficit for stranded other comprehensive income taxes arising from tax reform (a)	[1]						32.2
Ending Balance		(2,709.4)		(2,639.6)		(2,709.4)	(2,639.6)	(2,711.8)
AOCI Attributable to Parent
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			$ (173.7)		$ (90.3)	(173.7)	(90.3)	(171.0)
Other comprehensive income (loss)						(1.8)	(51.2)	80.7
Reclassification adjustment to accumulated deficit for stranded other comprehensive income taxes arising from tax reform (a)	[1]						(32.2)
Ending Balance		$ (175.5)		$ (173.7)		$ (175.5)	$ (173.7)	$ (90.3)
Treasury Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance			0.0		0.0	0.0	0.0	(0.1)
Beginning Balance			$ 0.0		$ 0.0	$ 0.0	$ 0.0	$ (0.5)
Shares purchased under employee plans and other								0.1
Shares purchased under employee plans and other								$ 0.5
Balance		0.0		0.0		0.0	0.0	0.0
Ending Balance		$ 0.0		$ 0.0		$ 0.0	$ 0.0	$ 0.0

[1] Per ASU 2018-02, entities can elect to make a one-time reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from newly enacted corporate tax rates under the Tax Cuts and Jobs Act. The Company elected to make the change and recorded the adjustment in 2017.