Description of Business and Accounting Policies Description of Business and Accounting Policies (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) d shares	Dec. 31, 2015 USD ($) shares	Dec. 31, 2014 USD ($)	Oct. 05, 2016 USD ($) shares	Oct. 04, 2016 shares	Jan. 24, 2013 shares
Description of accounting policies [Line Items]
Common Stock, Shares, Issued, Before Reverse Stock Split | shares					210,275,005
Common Stock, Shares, Issued | shares	42,056,237	42,003,600		42,055,001
Total Par Value, Amount, Reclassified				$ 1.7
Entity Number of Employees	3,400
Percent of Revenue from Foreign Subsidiaries	1.00%
Investment owned in CyrusOne Inc., Balance, Shares | shares						1,900,000
Investment owned in CyrusOne Inc., Percentage, Common Stock						8.60%
Investment owned in Equity Method Investee, Balance, Partnership Units | shares		6,300,000				42,600,000
Available for sale securities, ownership percentage		9.50%
Investment owned in Available for Sale Securities, Balance, Shares | shares	2,800,000	6,900,000
Investment owned in CyrusOne LP, Percentage, Partnership Units						66.00%
Total ownership interests in CyrusOne, Percentage						69.00%
Available-for-sale Securities	$ 128.0
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, before Tax	105.0
Cost Method Investments	3.4	$ 3.0
Proceeds from sale of wireless spectrum licenses	$ 0.0	$ 0.0	$ 194.4
Trade Receivables Due From Customers, Range, Minimum | d	21
Trade Receivables Due from Customers, Range, Maximum | d	90
Number of customers, exceeds 10% of total accounts receivable	1
Accounts Receivable from one customer greater than 10%, percentage	21.00%	22.00%
Number of customers, exceeds 10% of total revenue	1
Revenue from one customer greater than 10%, percentage	12.00%	12.00%	14.00%
Unbilled Receivables, Current	$ 14.5	$ 14.0
Payments to Acquire Equity Method Investments			$ 5.5
Customer Contract, Lower Range, in Years	1
Customer Contract, Upper Range, in Years	3
Advertising Expense	$ 9.5	8.3	7.2
Regulatory Taxes Included in Revenue	16.3	15.5	15.2
Regulatory Taxes Included in Expense	$ 17.5	$ 17.9	$ 16.4
Lower range, in years, of remaining service life of active employees	9
Upper range, in years, of remaining service life of active employees	13
Company Employees Participating in Collective Bargaining Agreement, Percentage	30.00%
Other Postretirement Benefit Plans, Defined Benefit [Member]
Description of accounting policies [Line Items]
Average life expectancy of retirees, in years	17