Long-Term Debt, Financing and Capital Lease Obligations (Narrative) (Details)		1 Months Ended				6 Months Ended
	Nov. 01, 2019 USD ($)	Nov. 06, 2018 USD ($)	Feb. 28, 2017	Oct. 31, 2016 USD ($)	May 31, 2016 USD ($)	Sep. 30, 2019 USD ($) site years	Sep. 30, 2018 USD ($)	Dec. 31, 2019	Sep. 16, 2019 USD ($)	May 01, 2019 USD ($)	Apr. 01, 2019 USD ($)	Mar. 31, 2019 USD ($) site	Feb. 26, 2019 USD ($)	Nov. 26, 2018 USD ($)	Oct. 01, 2018 USD ($)	Feb. 20, 2018	Feb. 02, 2017 USD ($)
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross														$ 8,000,000,000.0			$ 6,000,000,000.0
Long-term debt issued by 100% owned subsidiary and is fully and unconditionally guaranteed by the parent						$ 19,900,000,000
Interest Costs Capitalized						35,000,000	$ 34,000,000
Cash interest payments						1,200,000,000	$ 1,300,000,000
Redeemable notes						27,900,000,000
Principal amount of notes with the right to require the Company to repurchase on change of control						23,500,000,000
Current portion of long-term debt, financing and capital lease obligations						4,101,000,000					$ 4,514,000,000	$ 4,557,000,000
Operating Leases, Future Minimum Payments Due												$ 11,767,000,000
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						670,000,000									$ 2,000,000,000.0
Receivables Facility, repayments		$ 700,000,000
Maximum Funding Limit, increase						200,000,000
Receivables Facility, Amount Drawn on Facility						3,200,000,000
Sale Leaseback Transaction, Cumulative Lease Payments						$ 3,100,000,000
Long-term Debt, Percentage Bearing Variable Interest, Amount														300			250
Number of cell sites leased back | site						1,750						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						$ 1,110,000,000						$ 926,000,000
Installment Lease Receivables, Net Book Value						6,300,000,000
Capital Lease Obligations [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross												538,000,000
Finance lease obligations [Domain]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross						24,000,000
Other Debt Obligations [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross						$ 241,000,000
Tower financing
Schedule of Capitalization, Long-term Debt [Line Items]
Sale Leaseback Transaction, Net Book Value												109,000,000
Maximum | Capital Lease Obligations [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage						12.00%
Minimum | Capital Lease Obligations [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage						2.35%
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						$ 131,000,000
Shentel [Member] | Maximum | Capital Lease Obligations [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt instrument term					6 years
Shentel [Member] | Minimum | Capital Lease Obligations [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt instrument term					5 years
Delcredere / Ducroire (D/D) Secured Equipment Credit Facility [Member] | Line of Credit [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Repayments of Lines of Credit						20,000,000
Line of Credit Facility, Amount Outstanding						99,000,000
K-sure Secured Equipment Credit Facility [Member] | Line of Credit [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Repayments of Lines of Credit						72,000,000
Line of Credit Facility, Amount Outstanding						474,000,000
Line of credit facility, year-to-date amount drawn						96,000,000
Finnvera Secured Equipment Credit Facility [Member] | Line of Credit [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Repayments of Lines of Credit						41,000,000
Line of Credit Facility, Amount Outstanding						51,000,000
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						0			$ 300,000,000
Secured Revolving Bank Credit Facility expires in Feb 2021[Member] [Member] | Secured term loan [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Repayments of Lines of Credit						20,000,000
Line of Credit Facility, Amount Outstanding						3,900,000,000
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																	$ 2,000,000,000.0
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, 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						116,000,000
Sprint Nextel Corporation [Member] | Secured term loan [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross														2,000,000,000.0			$ 4,000,000,000.0
Incremental Term Loan borrowing													$ 900,000,000	$ 1,100,000,000
Debt instrument term			7 years
Line of Credit Facility, Amount Outstanding						5,885,000,000						5,915,000,000
Sprint Nextel Corporation [Member] | Senior Notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross						4,780,000,000						4,780,000,000
Sprint Nextel Corporation [Member] | Guaranteed notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross						$ 1,000,000,000						1,000,000,000
Sprint Nextel Corporation [Member] | Maximum | Senior Notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage						11.50%
Sprint Nextel Corporation [Member] | Minimum | Senior Notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage						6.00%
Sprint Nextel Corporation [Member] | Minimum | Guaranteed notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage						7.00%
PRWireless HoldCo, LLC Secured Term Loan [Member] | Secured term loan [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Line of Credit Facility, Amount Outstanding						$ 199,000,000						198,000,000
PRWireless HoldCo, LLC Secured Term Loan [Member] | Subsequent Event [Member] | Secured term loan [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Repayments of Lines of Credit	$ 199,000,000
Spectrum Financing [Member] | Secured Debt [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Maximum Borrowing Capacity				$ 7,000,000,000.0
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]
Long-term Debt, Gross						5,688,000,000						6,125,000,000
Debt Instrument, Interest Rate, Stated Percentage				3.36%
Debt instrument face amount				$ 3,500,000,000
Debt instrument term				5 years
Repayments of Debt						437,000,000
Secured Debt, Current						$ 875,000,000
Operating Leases, Future Minimum Payments Due				$ 3,500,000,000
Sprint Spectrum Co LLC, Sprint Spectrum Co II LLC, Sprint Spectrum Co III LLC [Member] | Maximum | Secured Debt [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage						5.15%
Sprint Spectrum Co LLC, Sprint Spectrum Co II LLC, Sprint Spectrum Co III LLC [Member] | Minimum | Secured Debt [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage						3.36%
Sprint Financing maturing 2021 [Member] | Secured Debt [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross						$ 1,800,000,000
Sprint Corporation [Member] | Senior Notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross						$ 12,000,000,000						12,000,000,000
Debt Instrument, Interest Rate, Stated Percentage																7.625%
Sprint Corporation [Member] | Maximum | Senior Notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage						7.88%
Sprint Corporation [Member] | Minimum | Senior Notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage						7.13%
Sprint Capital Corporation [Member] | Senior Notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross						$ 4,475,000,000				$ 1,700,000,000		$ 6,204,000,000
Debt Instrument, Interest Rate, Stated Percentage										6.90%
Sprint Capital Corporation [Member] | Maximum | Senior Notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage						8.75%
Sprint Capital Corporation [Member] | Minimum | Senior Notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage						6.88%
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%
Installment Receivables [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Purchase Commitment Allocation						78.00%
Accounts and notes receivable, net
Schedule of Capitalization, Long-term Debt [Line Items]
Financing Receivable, Net						$ 845,000,000						679,000,000
Accounts and notes receivable, net | Wireless Services and Installment Receivables [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Financing Receivable, Net						2,700,000,000
Other assets
Schedule of Capitalization, Long-term Debt [Line Items]
Financing Receivable, Net						265,000,000						247,000,000
Other assets | Special purpose entity [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Financing Receivable, Net						248,000,000
Interest Rate Swap [Member] | Sprint Nextel Corporation [Member] | Secured term loan [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Derivative Liability, Fair Value, Gross Liability						$ 22,000,000						$ 13,000,000
Derivative Liability																	$ 2,000,000,000.0
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%