Property, Plant and Equipment - Summary of Net Property, Plant and Equipment (Details) (Distribution Systems, USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	5,997.2	$ 5,956.7
Less accumulated depreciation	(3,466.8)	(3,384.9)
Net property, plant and equipment	2,530.4	2,571.8
Land
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	33.0	33.0
Building and Improvements
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	308.4	305.5
Poles
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	223.4	223.0
Fiber
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	1,850.7	1,841.2
Copper
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	3,439.0	3,430.8
Conduit
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	89.5	89.2
Construction in progress
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	53.2	$ 34.0
Minimum | Building and Improvements
Property Plant And Equipment [Line Items]
Depreciable Lives	3 years
Minimum | Poles
Property Plant And Equipment [Line Items]
Depreciable Lives	13 years
Minimum | Fiber
Property Plant And Equipment [Line Items]
Depreciable Lives	7 years
Minimum | Copper
Property Plant And Equipment [Line Items]
Depreciable Lives	7 years
Minimum | Conduit
Property Plant And Equipment [Line Items]
Depreciable Lives	13 years
Maximum | Building and Improvements
Property Plant And Equipment [Line Items]
Depreciable Lives	40 years
Maximum | Poles
Property Plant And Equipment [Line Items]
Depreciable Lives	40 years
Maximum | Fiber
Property Plant And Equipment [Line Items]
Depreciable Lives	40 years
Maximum | Copper
Property Plant And Equipment [Line Items]
Depreciable Lives	40 years
Maximum | Conduit
Property Plant And Equipment [Line Items]
Depreciable Lives	47 years