Basis of Presentation Basis of Presentation (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2015
Change in Accounting Estimate [Line Items]
Change in net income for change in accounting estimate	$ (205)	$ (188)	$ (540)	$ (584)
Unamortized debt issuance costs	182		182
Network assets, future abandonment | Service life
Change in Accounting Estimate [Line Items]
Depreciation	12		36
Change in net income for change in accounting estimate	$ (7)		$ (22)
Earnings per share, basic and diluted	$ (0.01)		$ (0.04)
Network assets, future abandonment | Forecast | Service life
Change in Accounting Estimate [Line Items]
Depreciation					$ 48
Change in net income for change in accounting estimate					$ (30)
Earnings per share, basic and diluted					$ (0.05)