Long-Term Debt, Financing and Capital Lease Obligations (Narrative) (Details)	1 Months Ended			2 Months Ended	9 Months Ended	12 Months Ended
	Feb. 28, 2017	Oct. 31, 2016 USD ($)	May 31, 2016 USD ($)	May 24, 2019 USD ($)	Dec. 31, 2017	Mar. 31, 2019 USD ($) site	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)	Mar. 31, 2020	Dec. 31, 2019	Apr. 01, 2019 USD ($)	Feb. 26, 2019 USD ($)	Dec. 31, 2018 USD ($)	Nov. 26, 2018 USD ($)	Nov. 01, 2018 USD ($) Rate	Feb. 20, 2018	Feb. 02, 2017 USD ($)	Nov. 30, 2015 USD ($)	Jan. 01, 2008 site
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term debt, gross														$ 8,000,000,000			$ 6,000,000,000
Long-term debt issued by 100% owned subsidiary and is fully and unconditionally guaranteed by the parent						$ 21,900,000,000
Secured debt						16,100,000,000
Interest costs capitalized						74,000,000	$ 55,000,000	$ 44,000,000
Cash interest payments						$ 2,600,000,000	$ 2,500,000,000	$ 2,700,000,000
Senior notes weighted average effective interest rate						6.50%	6.20%	6.40%
Redeemable notes						$ 30,100,000,000
Principal amount of notes with the right to require the Company to repurchase on change of control						23,900,000,000
Current portion of long-term debt, financing and capital lease obligations						4,557,000,000	$ 3,429,000,000
Receivables Facility, Repayment Under Facility						6,700,000,000
Installment receivables, net						926,000,000	1,149,000,000
Receivables Facility, Amount Drawn on Facility						$ 6,900,000,000
Receivables Facility, maximum amount available based on receivables sold to investors, percent						50.00%
Receivables Facility, Amount Outstanding						$ 2,600,000,000
Receivables Facility, Amount of Funds Available						900,000,000
Maximum funding limit, increase						$ 200,000,000
Maximum Funding Limit																		$ 4,500,000,000
Number of cell sites leased back | site						1,750													3,000
Ratio of total indebtedness to adjusted EBITDA						2.5
Long-term Debt, Percentage Bearing Variable Interest, Amount														300			250
Payments for (Proceeds from) Businesses and Interest in Affiliates			$ 181,000,000
Installment Lease Receivables, Net Book Value						$ 6,600,000,000
Secured Notes [Member] | Spectrum Financing [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
Secured Notes [Member] | Spectrum Financing maturing 2025 [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
Secured Notes [Member] | Spectrum Financing maturing 2028 [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
Secured Notes [Member] | Sprint Spectrum Co LLC, Sprint Spectrum Co II LLC, Sprint Spectrum Co III LLC [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term debt, gross						6,125,000,000	7,000,000,000
Repayments of Debt						875,000,000
Debt instrument, interest rate, stated percentage		3.36%
Secured Debt, Current						875,000,000
Aggregate cap		$ 3,500,000,000
Debt Instrument, Term		5 years
Debt instrument, face amount		$ 3,500,000,000
Secured Notes [Member] | Sprint Financing maturing 2021 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term debt, gross						2,200,000,000
Secured term loan [Member] | Sprint Nextel Corporation Guaranteed Notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term debt, gross						3,900,000,000								2,000,000,000			4,000,000,000
Incremental Term Loan borrowing												$ 900,000,000		$ 1,100,000,000
Repayments of Debt						40,000,000
Debt Instrument, Term	7 years
Line of credit facility, amount outstanding						5,915,000,000	3,960,000,000
Secured term loan [Member] | PRWireless HoldCo, LLC Secured Term Loan [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Repayments of Debt						2,000,000
Proceeds from Lines of Credit						18,000,000
Line of Credit Facility, Remaining Borrowing Capacity						2,000,000
Line of credit facility, amount outstanding						198,000,000	182,000,000
Senior Notes [Member] | Sprint Corporation [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%
Senior Notes [Member] | Sprint Nextel Corporation Guaranteed Notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term debt, gross						4,780,000,000	4,980,000,000
Current portion of long-term debt, financing and capital lease obligations													$ 200,000,000
Debt instrument, interest rate, stated percentage													9.25%
Line of Credit [Member] | Export Development Canada Credit Facilities [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Line of credit facility, amount outstanding						300,000,000	300,000,000
Line of Credit [Member] | Finnvera Secured Equipment Credit Facility [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Line of credit facility, amount outstanding						92,000,000
Debt instrument, annual principal payment						82,000,000
Line of Credit [Member] | K-sure Secured Equipment Credit Facility [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Line of credit facility, amount outstanding						450,000,000
Line of credit facility, year-to-date amount drawn						331,000,000
Debt instrument, annual principal payment						75,000,000
Line of Credit [Member] | Delcredere / Ducroire (D/D) Secured Equipment Credit Facility [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Repayments of Lines of Credit						40,000,000
Line of credit facility, amount outstanding						119,000,000
Guaranteed Notes [Member] | Sprint Nextel Corporation Guaranteed Notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term debt, gross						1,000,000,000	2,753,000,000								$ 1,800,000,000
Debt instrument, interest rate, stated percentage | Rate															9.00%
Revolving Credit Facility [Member] | Unsecured Revolving Credit Facility expires in 2018 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Line of Credit Facility, Remaining Borrowing Capacity						1,900,000,000
Line of credit facility, amount outstanding						0	0
Revolving Credit Facility [Member] | Secured Revolving Bank Credit Facility expires in Feb 2021[Member] [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity																	2,000,000,000
Letter of Credit [Member] | Unsecured Revolving Credit Facility expires in 2018 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Letters of credit outstanding, amount						118,000,000
Capital Lease Obligations [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term debt, gross						278,000,000
Capital Lease Obligations [Member] | Shentel [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term debt, gross						151,000,000
Parent [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term debt, gross						12,000,000,000
Current portion of long-term debt, financing and capital lease obligations						0	0
Spectrum Assets [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Concentration Risk, Percentage		14.00%
Interest Rate Swap [Member] | Secured term loan [Member] | Sprint Nextel Corporation Guaranteed Notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Derivative, Term of Contract								5 years
Derivative, Notional Amount																	$ 2,000,000,000
Derivative Asset, Fair Value, Gross Asset						$ 13,000,000
Derivative Liability, Fair Value, Gross Liability							41,000,000
London Interbank Offered Rate (LIBOR) [Member] | Secured term loan [Member] | PRWireless HoldCo, LLC Secured Term Loan [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Basis Spread on Variable Rate					5.25%
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%
Scenario, Forecast [Member] | Revolving Credit Facility [Member] | Secured Revolving Bank Credit Facility expires in Feb 2021[Member] [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Ratio of total indebtedness to adjusted EBITDA									3.5	3.75
Accounts and notes receivable, Net [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Installment receivables, net						$ 679,000,000	995,000,000
Accounts and notes receivable, Net [Member] | Wireless Services and Installment Receivables [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Installment receivables, net						2,500,000,000
Other Noncurrent Assets [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Installment receivables, net						247,000,000	$ 154,000,000
Other Noncurrent Assets [Member] | Special purpose entity [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Installment receivables, net						$ 231,000,000
Minimum [Member] | Secured Notes [Member] | Sprint Spectrum Co LLC, Sprint Spectrum Co II LLC, Sprint Spectrum Co III LLC [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt instrument, interest rate, stated percentage						3.36%
Minimum [Member] | Senior Notes [Member] | Sprint Corporation [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt instrument, interest rate, stated percentage						7.13%
Minimum [Member] | Senior Notes [Member] | Sprint Nextel Corporation Guaranteed Notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt instrument, interest rate, stated percentage						6.00%
Minimum [Member] | Guaranteed Notes [Member] | Sprint Nextel Corporation Guaranteed Notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt instrument, interest rate, stated percentage						7.00%
Minimum [Member] | Capital Lease Obligations [Member] | Shentel [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Term			5 years
Maximum [Member] | Secured Notes [Member] | Sprint Spectrum Co LLC, Sprint Spectrum Co II LLC, Sprint Spectrum Co III LLC [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt instrument, interest rate, stated percentage						5.15%
Maximum [Member] | Senior Notes [Member] | Sprint Corporation [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt instrument, interest rate, stated percentage						7.88%
Maximum [Member] | Senior Notes [Member] | Sprint Nextel Corporation Guaranteed Notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt instrument, interest rate, stated percentage						11.50%
Maximum [Member] | Capital Lease Obligations [Member] | Shentel [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Term			6 years
Subsequent Event [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Receivables Facility, Amount of Funds Available											$ 1,800,000,000
Receivables Facility, repayments				$ 800,000,000
Tower financing [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Sale Leaseback Transaction, Net Book Value						$ 109,000,000