Debt and Other Obligations Schedule of Extinguishment of Long Term Debt (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Extinguishment of Debt [Line Items]
Gain (Loss) on Extinguishment of Debt		$ (3)	$ 0	$ (74)	$ (4)
January 2010 Tower Revenue Notes [Member]
Extinguishment of Debt [Line Items]
Extinguishment of Debt, Amount				1,250
Repayments of Debt	[1]			1,318
Gain (Loss) on Extinguishment of Debt	[2]			(71)
2016 Term Loan A [Member]
Extinguishment of Debt [Line Items]
Extinguishment of Debt, Amount				0
Repayments of Debt				0
Gain (Loss) on Extinguishment of Debt	[3]			$ (3)

[1] Exclusive of accrued interest

[2] Inclusive of the write off of respective deferred financing costs.

[3] {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOjMwYmFhYmQzNDhkYzQ5ZjlhODZmNmE5MzJmNTUyNmYyfFRleHRTZWxlY3Rpb246ODBBNUUwNDQzQUVGOTIyRUMyMTZDRDM2Rjc1MTAyNTkM}