Commitments and Contingencies (Narrative) (Details) $ in Millions		3 Months Ended			6 Months Ended	12 Months Ended
	Apr. 19, 2012 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Mar. 31, 2013 USD ($)	Jul. 10, 2013 USD ($)	Mar. 31, 2016 USD ($) renewal_option	Mar. 31, 2015 USD ($)	Dec. 31, 2013 USD ($)
Commitments and Contingencies [Line Items]
Minimum spectrum reconfiguration obligations						$ 2,800
Total Payments directly attributable to performance under Report and Order						$ 3,500
Noncancelable portion of leases, maximum						15 years
Number of operating lease renewals available | renewal_option						1
Operating lease, maximum contract length to become eligible for renewal contract, term						10 years
General initial term of operating lease, minimum						5 years
General initial term of operating lease, maximum						12 years
Number of cell site renewal options available | renewal_option						5.0
Years for each renewal option for cell site leases						5 years
Maximum length of spectrum lease agreements						30 years
Maximum remaining commitments of other spectrum commitments						$ 86
Predecessor [Member]
Commitments and Contingencies [Line Items]
Operating leases, rent expense, net				$ 483	$ 1,000
Successor [Member]
Commitments and Contingencies [Line Items]
Payments directly attributable to performance under report and order, net change						75
Licensees reimbursed share of costs		$ 95
Operating leases, rent expense, net			$ 653			2,900	$ 2,600	$ 1,300
Payment to satisfy other spectrum commitments						$ 4
Minimum [Member]
Commitments and Contingencies [Line Items]
Remaining other spectrum commitments expected to be incurred over term						15 years
Maximum [Member]
Commitments and Contingencies [Line Items]
Remaining other spectrum commitments expected to be incurred over term						30 years
Letter Of Credit Required By The FCCs Report And Order [Member] | Unsecured Revolving Credit Facility expires in 2018 [Member]
Commitments and Contingencies [Line Items]
Initial letter of credit requirement						$ 2,500
Letters of credit outstanding, amount						256
New York sales taxes on receipts from sale of wireless services [Member]
Commitments and Contingencies [Line Items]
Sales receipts alleged to not be reported, amount	$ 100
Loss Contingency Accrual, Provision						$ 180