Long-Term Debt, Financing and Capital Lease Obligations (Narrative) (Details)	1 Months Ended				2 Months Ended	3 Months Ended			9 Months Ended	12 Months Ended
	Feb. 28, 2017	Oct. 31, 2016 USD ($)	May 31, 2016 USD ($)	Apr. 30, 2016 USD ($)	May 24, 2018 USD ($)	Mar. 31, 2018 USD ($) site	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Mar. 31, 2018 USD ($) site	Mar. 31, 2017 USD ($)	Mar. 31, 2016 USD ($)	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jun. 01, 2018	Apr. 01, 2018 USD ($)	Feb. 20, 2018 USD ($)	Feb. 02, 2017 USD ($)	Nov. 30, 2015 USD ($)	Nov. 19, 2015 USD ($)	Feb. 24, 2015 USD ($)	Dec. 31, 2014 USD ($) tranche	Sep. 11, 2013 USD ($)	Jan. 01, 2008 site
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term debt, gross																			$ 6,000,000,000
Long-term debt issued by 100% owned subsidiary and is fully and unconditionally guaranteed by the parent						$ 21,600,000,000				$ 21,600,000,000
Secured debt						14,800,000,000				14,800,000,000
Interest costs capitalized										55,000,000	$ 44,000,000	$ 51,000,000
Cash interest payments										$ 2,500,000,000	$ 2,700,000,000	2,400,000,000
Senior notes weighted average effective interest rate										6.20%	6.40%
Redeemable notes						32,700,000,000				$ 32,700,000,000
Principal amount of notes with the right to require the Company to repurchase on change of control						26,500,000,000				26,500,000,000
Receivables Facility, Repayment Under Facility										2,200,000,000
Receivables Facility, repurchase of receivables										3,100,000,000	$ 1,400,000,000	1,200,000,000
Installment receivables, net						1,149,000,000				1,149,000,000	1,764,000,000
Receivables Facility, Amount Drawn on Facility										2,700,000,000
Aggregate cap						$ 13,002,000,000				13,002,000,000
Call premiums paid on debt redemptions										$ 131,000,000	0	0
Receivables Facility, maximum amount available based on receivables sold to investors, percent						50.00%				50.00%
Receivables Facility, Amount Outstanding						$ 2,400,000,000				$ 2,400,000,000
Receivables Facility, Amount of Funds Available						$ 1,200,000,000				1,200,000,000
Repayments of Accounts Receivable Securitization										$ 385,000,000
Maximum Funding Limit																				$ 4,300,000,000
Number of cell sites leased back | site						2,000				2,000															3,000
Ratio of total indebtedness to adjusted EBITDA						2.5				2.5
Long-term Debt, Percentage Bearing Variable Interest, Amount																			250
Sale Leaseback Transaction, Net Book Value																					$ 1,300,000,000
Payments for (Proceeds from) Businesses and Interest in Affiliates			$ 181,000,000
Proceeds from sale-leaseback transaction										$ 0	0	1,136,000,000
Gain (Loss) on Extinguishment of Debt										(65,000,000)	0	0
Installment Lease Receivables, Net Book Value						$ 6,000,000,000				6,000,000,000
Finnvera Secured Equipment Credit Facility [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Line of Credit Facility, Increase (Decrease), Net									$ 160,000,000
Delcredere / Ducroire (D/D) Secured Equipment Credit Facility [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Line of Credit Facility, Increase (Decrease), Net										150,000,000
Exchangeable Notes [Member] | Clearwire Communications LLC [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term debt, gross						$ 0				$ 0	629,000,000
Debt instrument, interest rate, stated percentage						8.25%				8.25%
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				$ 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%				4.738%
Debt Instrument, Additional Borrowings Available						$ 2,100,000,000				$ 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%				5.152%
Debt Instrument, Additional Borrowings Available						$ 1,800,000,000				$ 1,800,000,000
Secured Notes [Member] | Sprint Nextel Corporation Guaranteed Notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term debt, gross						$ 0				$ 0	200,000,000
Debt instrument, interest rate, stated percentage						9.25%				9.25%
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						$ 7,000,000,000				$ 7,000,000,000	3,500,000,000
Repayments of Debt										438,000,000
Debt instrument, interest rate, stated percentage		3.36%
Secured Debt, Current						875,000,000				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						3,100,000,000				3,100,000,000
Secured term loan [Member] | Sprint Nextel Corporation Guaranteed Notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term debt, gross						4,000,000,000				4,000,000,000									4,000,000,000
Repayments of Debt										40,000,000
Debt Instrument, Term	7 years
Line of credit facility, amount outstanding						3,960,000,000				3,960,000,000	4,000,000,000
Secured term loan [Member] | PRWireless HoldCo, LLC Secured Term Loan [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Repayments of Debt										1,000,000
Proceeds from Lines of Credit										5,000,000
Line of Credit Facility, Remaining Borrowing Capacity						20,000,000				20,000,000
Line of credit facility, amount outstanding						182,000,000	$ 178,000,000		182,000,000	182,000,000	0
Senior Notes [Member] | Notes due 2017 and Guaranteed Notes Due 2018 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Unamortized Premium								$ 66,000,000
Call premiums paid on debt redemptions								131,000,000
Gain (Loss) on Extinguishment of Debt								65,000,000
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	10,500,000,000
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						4,980,000,000				4,980,000,000	6,080,000,000
Senior Notes [Member] | Notes due 2017 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Repayments of Debt								$ 388,000,000
Debt instrument, interest rate, stated percentage							8.375%	8.375%
Extinguishment of Debt, Amount							$ 912,000,000
Senior Notes [Member] | Sprint Corporation 7.625% [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt instrument, interest rate, stated percentage																						7.625%		7.25%
Debt instrument, face amount																		$ 1,500,000,000				$ 1,500,000,000		$ 2,250,000,000
Senior Notes [Member] | Guaranteed Notes Due 2018 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Repayments of Debt						0		$ 1,200,000,000
Debt instrument, interest rate, stated percentage								9.00%
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	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, maximum borrowing capacity																							$ 800,000,000
Line of credit facility, amount outstanding						174,000,000				174,000,000
Debt instrument, annual principal payment										126,000,000
Line of Credit [Member] | K-sure Secured Equipment Credit Facility [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity																							$ 750,000,000
Line of credit facility, amount outstanding						194,000,000				194,000,000
Debt instrument, annual principal payment										65,000,000
Number of tranches | tranche																							3
Line of Credit [Member] | Delcredere / Ducroire (D/D) Secured Equipment Credit Facility [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity							$ 150,000,000																$ 250,000,000
Repayments of Lines of Credit										23,000,000
Line of credit facility, amount outstanding						159,000,000				159,000,000
Guaranteed Notes [Member] | Sprint Nextel Corporation Guaranteed Notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term debt, gross						2,753,000,000				2,753,000,000	4,000,000,000
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						1,800,000,000				1,800,000,000
Line of credit facility, amount outstanding						0				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						151,000,000				151,000,000
Capital Lease Obligations [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term debt, gross						347,000,000				347,000,000
Capital Lease Obligations [Member] | Shentel [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term debt, gross						138,000,000				138,000,000
Parent [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term debt, gross						12,000,000,000				12,000,000,000
Call premiums paid on debt redemptions										0
Proceeds from sale-leaseback transaction												0
Spectrum Assets [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Concentration Risk, Percentage		14.00%
MLS 2nd Tranche [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Sale Leaseback Transaction, Net Book Value			$ 1,300,000,000
Proceeds from sale-leaseback transaction				$ 1,100,000,000
Tower financing [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Sale Leaseback Transaction, Net Book Value									$ 150,000,000
Network Sale-Leaseback [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Repayments of Debt										1,900,000,000
Proceeds from sale-leaseback transaction				2,200,000,000
Handset Sale-Leaseback Tranche 2 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Receivables from sale-leaseback				$ 186,000,000
Handset Sale-Leaseback Tranche 1 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Sale Leaseback Transaction, Monthly Rental Payments											$ 494,000,000	$ 277,000,000
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						$ 41,000,000				$ 41,000,000
Derivative Liability, Fair Value, Gross Liability											$ (2,000,000)
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						26.00%				26.00%
Installment Receivables [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Purchase Commitment Allocation						28.00%				28.00%
Future lease receivables [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Purchase Commitment Allocation						46.00%				46.00%
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	4.75
Scenario, Forecast [Member] | Wireless Service [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Purchase Commitment Allocation																26.00%
Scenario, Forecast [Member] | Installment Receivables [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Purchase Commitment Allocation																18.00%
Scenario, Forecast [Member] | Future lease receivables [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Purchase Commitment Allocation																56.00%
Accounts and notes receivable, Net [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Installment receivables, net						$ 995,000,000				$ 995,000,000	1,195,000,000
Accounts and notes receivable, Net [Member] | Wireless Services and Installment Receivables [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Installment receivables, net						2,800,000,000				2,800,000,000
Other Noncurrent Assets [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Installment receivables, net						154,000,000				154,000,000	$ 569,000,000
Other Noncurrent Assets [Member] | Special purpose entity [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Installment receivables, net						$ 147,000,000				$ 147,000,000
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%				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%				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%				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%				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%				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%				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%				11.50%
Maximum [Member] | Guaranteed Notes [Member] | Sprint Nextel Corporation Guaranteed Notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt instrument, interest rate, stated percentage						9.00%				9.00%
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																	$ 1,300,000,000
Receivables Facility, repayments					$ 1,100,000,000