Commitments and Contingencies (Narrative) (Details) $ in Millions	3 Months Ended
	Jun. 30, 2019 USD ($) claim	Mar. 31, 2019 USD ($)
Commitments and Contingencies [Line Items]
Minimum spectrum reconfiguration obligations | $	$ 2,800
Total Payments directly attributable to performance under Report and Order | $	3,600
Payments directly attributable to performance under report and order, net change related to FCC licenses | $	2
Unsecured Revolving Credit Facility expires in 2018 [Member] | Letter Of Credit Required By The FCCs Report And Order [Member]
Commitments and Contingencies [Line Items]
Initial Letter of Credit Requirement | $		$ 2,500
Letters of Credit Outstanding, Amount | $	$ 78
Derivative Shareholder Suits [Member]
Commitments and Contingencies [Line Items]
Loss Contingency, New Claims Filed, Number | claim	8
Louisiana Municipal Police Employees Retirement System [Member]
Commitments and Contingencies [Line Items]
Loss Contingency, Claims Dismissed, Number | claim	1
Johnson County Kansas [Member]
Commitments and Contingencies [Line Items]
Loss Contingency, New Claims Filed, Number | claim	2
Loss Contingency, Claims Dismissed, Number | claim	1
Federal Court of Kansas [Member]
Commitments and Contingencies [Line Items]
Loss Contingency, Pending Claims, Number | claim	5