Long-Term Debt, Financing and Capital Lease Obligations (Narrative) (Details)	1 Months Ended				3 Months Ended		12 Months Ended
	Aug. 07, 2018 USD ($)	Feb. 28, 2017	Oct. 31, 2016 USD ($)	May 31, 2016 USD ($)	Jun. 30, 2018 USD ($) site years	Jun. 30, 2017 USD ($)	Mar. 31, 2017	Dec. 31, 2019	Jul. 01, 2018 USD ($)	Jun. 01, 2018	May 31, 2018	Mar. 31, 2018 USD ($) site	Feb. 20, 2018	Sep. 30, 2017 USD ($)	Feb. 02, 2017 USD ($)	Nov. 30, 2015 USD ($)	Dec. 31, 2014 USD ($) tranche
Schedule of Capitalization, Long-term Debt [Line Items]
Maximum Funding Limit																$ 4,500,000,000
Receivables Facility, maximum amount available based on receivables sold to investors, percent					50.00%
Receivables Facility, Amount Outstanding					$ 2,700,000,000
Receivables Facility, Amount of Funds Available					942,000,000
Maximum Funding Limit, increase					200,000,000
Receivables Facility, Amount Drawn on Facility					1,400,000,000
Sale Leaseback Transaction, Cumulative Lease Payments					1,100,000,000
Long-term debt issued by 100% owned subsidiary and is fully and unconditionally guaranteed by the parent					21,800,000,000
Interest Costs Capitalized						$ 15,000,000
Cash interest payments					600,000,000	700,000,000
Redeemable notes					32,500,000,000
Principal amount of notes with the right to require the Company to repurchase on change of control					26,300,000,000
Call premiums paid on debt redemptions					0	129,000,000
Gain (Loss) on Extinguishment of Debt					$ 0	$ (66,000,000)
Long-term Debt, Gross															$ 6,000,000,000
Long-term Debt, Percentage Bearing Variable Interest, Amount															250
Number of cell sites leased back | site					2,000							3,000
Term in years for cell sites leased back renewal options | years					20
Payments for (Proceeds from) Businesses and Interest in Affiliates				$ 181,000,000
Ratio Of Total Indebtedness To Adjusted EBITDA					2.5
Financing Receivable, Net					$ 983,000,000							$ 1,149,000,000
Installment Lease Receivables, Net Book Value					6,200,000,000
Capital Lease Obligations [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross					327,000,000							686,000,000
Tower financing [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Sale Leaseback Transaction, Net Book Value					$ 139,000,000
Subsequent Event [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Receivables Facility, Amount of Funds Available									$ 1,500,000,000
Receivables Facility, repayments	$ 1,200,000,000
Minimum [Member] | Capital Lease Obligations [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage					2.35%
Maximum [Member] | Capital Lease Obligations [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage					12.00%
Spectrum Assets [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Concentration Risk, Percentage			14.00%
Shentel [Member] | Capital Lease Obligations [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross					$ 132,000,000
Delcredere / Ducroire (D/D) Secured Equipment Credit Facility [Member] | Line of Credit [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Aggregate principal amount line of credit														$ 150,000,000			$ 250,000,000
Repayments of Lines of Credit					20,000,000
Line of Credit Facility, Amount Outstanding					139,000,000
K-sure Secured Equipment Credit Facility [Member] | Line of Credit [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Aggregate principal amount line of credit																	$ 750,000,000
Repayments of Lines of Credit					32,000,000
Number of tranches | tranche																	3
Line of Credit Facility, Amount Outstanding					162,000,000
Finnvera Secured Equipment Credit Facility [Member] | Line of Credit [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Aggregate principal amount line of credit																	$ 800,000,000
Repayments of Lines of Credit					13,000,000
Line of Credit Facility, Amount Outstanding					161,000,000
Export Development Canada Agreement [Member] | Line of Credit [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Line of Credit Facility, Amount Outstanding												300,000,000
Export Development Canada Agreement [Member] | Tranche three and four [Member] | Line of Credit [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Line of Credit Facility, Amount Outstanding					300,000,000
Secured Revolving Bank Credit Facility expires in Feb 2021[Member] [Member] | Revolving Credit Facility [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Aggregate principal amount line of credit															$ 2,000,000,000
Line of Credit Facility, Remaining Borrowing Capacity					1,900,000,000
Line of Credit Facility, Amount Outstanding					0							0
Ratio Of Total Indebtedness To Adjusted EBITDA															4.8
Ratio Of Total Indebtedness To Adjusted EBITDA, Minimum															3.5
Secured Revolving Bank Credit Facility expires in Feb 2021[Member] [Member] | Letter of Credit [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Letters of Credit Outstanding, Amount					144,000,000
Sprint Nextel Corporation [Member] | Secured term loan [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross															$ 4,000,000,000
Line of Credit Facility, Amount Outstanding					3,950,000,000							3,960,000,000
Debt Instrument, Term		7 years
Sprint Nextel Corporation [Member] | Senior Notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross					4,980,000,000							4,980,000,000
Sprint Nextel Corporation [Member] | Guaranteed notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross					$ 2,753,000,000							2,753,000,000
Sprint Nextel Corporation [Member] | Minimum [Member] | Senior Notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage					6.00%
Sprint Nextel Corporation [Member] | Minimum [Member] | Guaranteed notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage					7.00%
Sprint Nextel Corporation [Member] | Maximum [Member] | Senior Notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage					11.50%
Sprint Nextel Corporation [Member] | Maximum [Member] | Guaranteed notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage					9.00%
PRWireless HoldCo, LLC Secured Term Loan [Member] | Secured term loan [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Line of Credit Facility, Remaining Borrowing Capacity					$ 20,000,000
Line of Credit Facility, Amount Outstanding					182,000,000							182,000,000
Spectrum Financing [Member] | Secured Debt [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Maximum Borrowing Capacity			$ 7,000,000,000
Debt Instrument, Additional Borrowings Available												3,900,000,000
Sprint Spectrum Co LLC, Sprint Spectrum Co II LLC, Sprint Spectrum Co III LLC [Member] | Secured Debt [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			3.36%
Operating Leases, Future Minimum Payments Due			$ 3,500,000,000
Repayments of Debt					219,000,000
Long-term Debt, Gross					6,781,000,000							7,000,000,000
Debt instrument face amount			$ 3,500,000,000
Debt Instrument, Term			5 years
Secured Debt, Current					$ 875,000,000
Sprint Spectrum Co LLC, Sprint Spectrum Co II LLC, Sprint Spectrum Co III LLC [Member] | Minimum [Member] | Secured Debt [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage					3.36%
Sprint Spectrum Co LLC, Sprint Spectrum Co II LLC, Sprint Spectrum Co III LLC [Member] | Maximum [Member] | Secured Debt [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage					5.15%
Sprint Financing maturing 2021 [Member] | Secured Debt [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross					$ 2,900,000,000
Sprint Corporation [Member] | Senior Notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage													7.625%
Long-term Debt, Gross					$ 12,000,000,000							$ 12,000,000,000
Sprint Corporation [Member] | Minimum [Member] | Senior Notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage					7.13%
Sprint Corporation [Member] | Maximum [Member] | Senior Notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage					7.88%
Spectrum Financing maturing 2025 [Member] | Secured Debt [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage												4.738%
Debt Instrument, Additional Borrowings Available												$ 2,100,000,000
Spectrum Financing maturing 2028 [Member] | Secured Debt [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage												5.152%
Debt Instrument, Additional Borrowings Available												$ 1,800,000,000
Wireless Service [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Purchase Commitment Allocation					22.00%					26.00%	26.00%
Installment Receivables [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Purchase Commitment Allocation					78.00%					18.00%	28.00%
Future lease receivables [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Purchase Commitment Allocation										56.00%	46.00%
Accounts and notes receivable, net
Schedule of Capitalization, Long-term Debt [Line Items]
Financing Receivable, Net					$ 841,000,000							995,000,000
Accounts and notes receivable, net | Wireless Services and Installment Receivables [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Financing Receivable, Net					2,600,000,000
Other assets
Schedule of Capitalization, Long-term Debt [Line Items]
Financing Receivable, Net					142,000,000							154,000,000
Other assets | Special purpose entity [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Financing Receivable, Net					132,000,000
Interest Rate Swap [Member] | Sprint Nextel Corporation [Member] | Secured term loan [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Derivative, Notional Amount															$ 2,000,000,000
Derivative Liability, Fair Value, Gross Liability					$ 55,000,000							$ 41,000,000
Derivative, Term of Contract							5 years
Scenario, Forecast [Member] | Secured Revolving Bank Credit Facility expires in Feb 2021[Member] [Member] | Revolving Credit Facility [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Ratio Of Total Indebtedness To Adjusted EBITDA								3.75
London Interbank Offered Rate (LIBOR) [Member] | PRWireless HoldCo, LLC Secured Term Loan [Member] | Secured term loan [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Basis Spread on Variable Rate					5.25%