Funding Sources	12 Months Ended
Mar. 31, 2017
Receivables [Abstract]
Funding Sources	Funding Sources Our device leasing and installment billing programs require a greater use of operating cash flows in the earlier part of the device contracts as our subscribers will generally pay less upfront than a traditional subsidy program. The Accounts Receivable Facility and the Handset Sale-Leaseback transactions described below were designed in large part to mitigate the significant use of cash from purchasing devices from OEMs to fulfill our installment billing and leasing programs. We entered into the Network Equipment Sale-Leaseback transaction in April 2016 to sell and leaseback certain network equipment to unrelated bankruptcy-remote SPEs that provided $2.2 billion in cash proceeds. In October 2016, we entered into a spectrum financing transaction whereby a portion of our spectrum holdings was used as collateral to issue $3.5 billion in senior secured notes. In February 2017, we entered into a new credit agreement for $6.0 billion, consisting of a $4.0 billion, seven-year secured term loan that matures in February 2024 and a $2.0 billion secured revolving bank credit facility that expires in February 2021. Accounts Receivable Facility Transaction Overview Our Accounts Receivable Facility (Receivables Facility) provides us the opportunity to sell certain wireless service receivables, installment receivables, and future amounts due from customers who lease certain devices from us to unaffiliated third parties (the Purchasers). The maximum funding limit under the Receivables Facility is $4.3 billion. While we have the right to decide how much cash to receive from each sale, the maximum amount of cash available to us varies based on a number of factors and currently represents approximately 50% of the total amount of the eligible receivables sold to the Purchasers. As of March 31, 2017, the total amount available to be drawn was $826 million. The Receivables Facility was amended in November 2016 to, among other things, reallocate the Purchasers' commitments between wireless service, installment and future lease receivables to 33%, 39% and 28%, respectively. The amendment was in response to changing trends in the financing methods selected by customers. In February 2017, the Receivables Facility was amended to extend the maturity date to November 2018. Additionally, Sprint gained effective control over the receivables transferred to the Purchasers by obtaining the right, under certain circumstances, to repurchase them. Subsequent to the February 2017 amendment, all proceeds received from the Purchasers in exchange for the transfer of our wireless service and installment receivables are recorded as borrowings and all cash inflows and outflows under the Receivables Facility are reported as financing activities in the consolidated statements of cash flows. As a result of the amendment, there was a non-cash derecognition of the deferred purchase price receivable (DPP) asset totaling $1.5 billion, along with corresponding increases to "Accounts and notes receivable, net" of $2.6 billion, "Other assets" of $563 million and "Long-term debt, financing and capital lease obligations" of $1.7 billion. During the year ended March 31, 2017 and subsequent to the February 2017 amendment, we elected to receive $100 million of cash and also remitted $161 million of funds to the Purchasers because the amount of cash proceeds received by us under the facility exceeded the maximum funding limit, which were reported as financing activities in the consolidated statements of cash flows. Prior to the February 2017 amendment, wireless service and installment receivables sold to the Purchasers were treated as a sale of financial assets and we derecognized these receivables, as well as the related allowances, and recognized the net proceeds received in cash provided by operating activities in the consolidated statements of cash flows. The total proceeds from the sale of these receivables were comprised of a combination of cash and a DPP. The DPP was realized by us upon either the ultimate collection of the underlying receivables sold to the Purchasers or upon Sprint's election to receive additional advances in cash from the Purchasers subject to the total availability under the Receivables Facility. The fees associated with these sales were recognized in "Selling, general and administrative" in the consolidated statements of operations through the date of the February 2017 amendment. Subsequent to the February 2017 amendment, the sale of wireless service and installment receivables are reported as financings, which is consistent with our historical treatment for the sale of future lease receivables, and the associated fees are recognized as "Interest expense" in the consolidated statements of operations. Transaction Structure Sprint contributes certain wireless service, installment and future lease receivables as well as the associated leased devices to Sprint's wholly-owned consolidated bankruptcy-remote SPEs. At Sprint's direction, the SPEs have sold, and will continue to sell, wireless service, installment and future lease receivables to Purchasers or to a bank agent on behalf of the Purchasers. Leased devices will remain with the SPEs, once sales are initiated, and continue to be depreciated over their estimated useful life. At March 31, 2017, wireless service and installment receivables contributed to the SPEs and included in "Accounts and notes receivable, net" in the consolidated balance sheets were $2.9 billion and the long-term portion of installment receivables included in "Other assets" in the consolidated balance sheets was $569 million. As of March 31, 2017, the net book value of devices contributed to the SPEs was approximately $3.1 billion. Each SPE is a separate legal entity with its own separate creditors who will be entitled, prior to and upon the liquidation of the SPE, to be satisfied out of the SPE’s assets prior to any assets in the SPE becoming available to Sprint. Accordingly, the assets of the SPE are not available to pay creditors of Sprint or any of its affiliates (other than any other SPE), although collections from these receivables in excess of amounts required to repay the advances, yield and fees of the Purchasers and other creditors of the SPEs may be remitted to Sprint during and after the term of the Receivables Facility. Sales of eligible receivables by the SPEs generally occur daily and are settled on a monthly basis. Sprint pays a fee for the drawn and undrawn portions of the Receivables Facility. A subsidiary of Sprint services the receivables in exchange for a monthly servicing fee, and Sprint guarantees the performance of the servicing obligations under the Receivables Facility. DPP Prior to the February 2017 amendment, the DPP was classified as a trading security within "Prepaid expenses and other current assets" in the consolidated balance sheets and was recorded at its estimated fair value. Subsequent to the February 2017 amendment, the Receivables Facility is accounted for as a financing and therefore the DPP is no longer recorded as a separate asset. The DPP related to our wireless service and installment receivables was $1.2 billion as of March 31, 2016. The fair value of the DPP was estimated using a discounted cash flow model, which relies principally on unobservable inputs such as the nature and credit class of the sold receivables and subscriber payment history, and, for installment receivables sold, the estimated timing of upgrades and upgrade payment amounts for those with upgrade options. Changes in the fair value of the DPP did not have a material impact on our consolidated statements of operations for the years ended March 31, 2017 and 2016. During the year ended March 31, 2017, prior to the February 2017 amendment, we remitted $270 million of funds to the Purchasers because the amount of cash proceeds received by us under the facility exceeded the maximum funding limit, which increased the total amount of the DPP due to Sprint. We also elected to receive $625 million of cash, which decreased the total amount of the DPP due to Sprint. In addition, during the year ended March 31, 2017, prior to the February 2017 amendment, sales of new receivables exceeded cash collections on previously sold receivables such that the DPP increased by $644 million. Variable Interest Entity Sprint determined that certain of the Purchasers, which are multi-seller asset-backed commercial paper conduits (Conduits) are considered variable interest entities because they lack sufficient equity to finance their activities. Sprint's interest in the receivables purchased by the Conduits is not considered a variable interest because it is in assets that represent less than 50% of the total activity of the Conduits. Handset Sale-Leasebacks In December 2015 and May 2016, we sold certain iPhone^® devices being leased by our customers to Mobile Leasing Solutions, LLC (MLS), a company formed by a group of equity investors, including SoftBank Group Corp. (SoftBank), and then subsequently leased the devices back. Under the agreements, Sprint generally maintains the customer leases, continues to collect and record lease revenue from the customer and remits monthly rental payments to MLS during the leaseback periods. Under the agreements, Sprint contributed the devices and the associated customer leases to wholly-owned consolidated bankruptcy-remote special purpose entities of Sprint (SPE Lessees). The SPE Lessees then sold the devices and transferred certain specified customer lease end rights and obligations, such as the right to receive the proceeds from customers who elect to purchase the device at the end of the customer lease term, to MLS in exchange for a combination of cash and DPP. Settlement for the DPP occurs near the end of the agreement and can be reduced to the extent that MLS experiences a loss on the device (either not returned or sold at an amount less than the expected residual value of the device), but only to the extent of the device's DPP balance. In the event that MLS sells the devices returned from our customers at a price greater than the expected device residual value, Sprint has the potential to share some of the excess proceeds. The SPE Lessees retain all rights to the underlying customer leases, such as the right to receive the rental payments during the device leaseback period, other than the aforementioned certain specified customer lease end rights. Each SPE Lessee is a separate legal entity with its own separate creditors who will be entitled, prior to and upon the liquidation of the SPE Lessee, to be satisfied out of the SPE Lessee’s assets prior to any assets in the SPE Lessee becoming available to Sprint. Accordingly, the assets of the SPE Lessee are not available to pay creditors of Sprint or any of its affiliates. The SPE Lessees are obligated to pay the full monthly rental payments under each device lease to MLS regardless of whether our customers make lease payments on the devices leased to them or whether the customer lease is canceled. Sprint has guaranteed to MLS the performance of the agreements and undertakings of the SPE Lessees under the transaction documents. Handset Sale-Leaseback Tranche 1 (Tranche 1) In December 2015, Sprint transferred devices with a net book value of approximately $1.3 billion to MLS in exchange for proceeds totaling $1.1 billion and a DPP of $126 million. We recorded the sale, removed the device from our balance sheet, and classified the leasebacks as operating leases. The difference between the fair value and the net book value of the devices sold was recognized as a loss on disposal of property, plant and equipment in the amount of $65 million and was included in "Other, net" in the consolidated statements of operations for the year ended March 31, 2016. The cash proceeds received in the transaction were reflected as cash provided by investing activities in the consolidated statements of cash flows and payments made to MLS under the leaseback are reflected as "Cost of products" in the consolidated statements of operations. Rent expense related to MLS totaled $494 million and $277 million during the years ended March 31, 2017 and 2016, respectively, and is reflected within cash flows from operations. In December 2016, Sprint terminated Tranche 1 by repurchasing the devices and related customer lease end rights and obligations from MLS for consideration of $375 million of net cash payments and the DPP of $126 million. As a result of the transaction, Sprint recorded $477 million of property, plant and equipment, $16 million of other assets, and was released from certain liabilities. Additionally, the leaseback was canceled and there will be no future rental payments owed to MLS related to Tranche 1. The impact to the consolidated statements of operations as a result of the termination was immaterial. Handset Sale-Leaseback Tranche 2 (Tranche 2) In May 2016, Sprint transferred devices with a net book value of approximately $1.3 billion to MLS in exchange for cash proceeds totaling $1.1 billion and a DPP of $186 million. Unlike Tranche 1, Tranche 2 was accounted for as a financing. Accordingly, the devices remain in "Property, plant and equipment, net" in the consolidated balance sheets and we continue to depreciate the assets to their estimated residual values over the respective customer lease terms. At March 31, 2017, the net book value of devices transferred to MLS was approximately $575 million. The proceeds received are reflected as cash provided by financing activities in the consolidated statements of cash flows and payments made to MLS will be reflected as principal repayments and interest expense. We have elected to account for the financing obligation at fair value. Accordingly, changes in the fair value of the financing obligation are recognized in "Other (expense) income, net" in the consolidated statements of operations over the course of the arrangement. Tranche 2 primarily includes devices from our iPhone Forever Program, whereas these devices were specifically excluded from Tranche 1. The iPhone Forever Program provides our leasing customers the ability to upgrade their devices and to enter into a new lease agreement, subject to certain conditions, upon Apple's release of a next generation device. Upon a customer exercising their iPhone Forever upgrade right, Sprint has the option to terminate the existing leaseback by immediately remitting all unpaid device leaseback payments and returning the device to MLS. Alternatively, Sprint has the option to transfer the title in the new device to MLS in exchange for the title in the original device (Exchange Option). If Sprint elects the Exchange Option, we are required to continue to pay existing device leaseback rental related to the original device, among other requirements. To address the introduction of the upgrade feature into the sale-leaseback structure, among other factors, numerous contractual terms from Tranche 1 were modified, which shifted certain risks of ownership in the devices away from MLS to Sprint and resulted in Tranche 2 being accounted for as a financing. For instance, the device leaseback periods are generally longer in Tranche 2 as compared to Tranche 1, and the resulting amounts committed to be paid by the Company represent the initial proceeds received from MLS plus interest. This mitigates MLS's exposure to certain risks for non-returned and damaged devices, as well as to declines in device residual values. Network Equipment Sale-Leaseback In April 2016, Sprint sold and leased back certain network equipment to unrelated bankruptcy-remote special purpose entities (collectively, "Network LeaseCo"). The network equipment was used as collateral to raise approximately $2.2 billion in borrowings from external investors, including SoftBank. Sprint's payments to Network LeaseCo during the leaseback period are used by Network LeaseCo to service debt. Network LeaseCo is a variable interest entity for which Sprint is the primary beneficiary. As a result, Sprint is required to consolidate Network LeaseCo and our consolidated financial statements include Network LeaseCo's debt and the related financing cash inflows. The network assets included in the transaction, which had a net book value of approximately $3.0 billion and consisted primarily of equipment located at cell towers, remain on Sprint's consolidated financial statements and continue to be depreciated over their respective estimated useful lives. At March 31, 2017, these network assets had a net book value of approximately $2.4 billion. The proceeds received were reflected as cash provided by financing activities in the consolidated statements of cash flows and payments made by Network LeaseCo are reflected as principal repayments and interest expense over the respective terms. Sprint has the option to purchase the equipment at the end of the leaseback term for a nominal amount. All intercompany transactions between Network LeaseCo and Sprint are eliminated in our consolidated financial statements. Principal and interest payments on the borrowings from the external investors will be repaid in staggered, unequal payments through January 2018. The first principal payment of $300 million was made in March 2017 with the remaining $1.9 billion of principal payments due in fiscal year 2017. Spectrum Financing In October 2016, Sprint transferred certain directly held and third-party leased spectrum licenses (collectively, "Spectrum Portfolio") to wholly-owned bankruptcy-remote special purpose entities (collectively, "Spectrum Financing SPEs"). The Spectrum Portfolio, which represents approximately 14% of Sprint's total spectrum holdings on a MHz-pops basis, was used as collateral to raise an initial $3.5 billion in senior secured notes at 3.36% per annum from external investors under a $7.0 billion program. Sprint can utilize this financing structure to potentially raise up to an additional $3.5 billion, subject to certain conditions. The notes will be repaid over a five-year term, with interest-only payments over the first four quarters and amortizing quarterly principal payments thereafter commencing in December 2017 through September 2021. Sprint Communications, Inc. simultaneously entered into a long-term lease with the Spectrum Financing SPEs for the ongoing use of the Spectrum Portfolio. Sprint Communications, Inc. is required to make monthly lease payments to the Spectrum Financing SPEs at a market rate. Those lease payments are sufficient to service the senior secured notes. As the Spectrum Financing SPEs are wholly-owned Sprint subsidiaries, these entities are consolidated and all intercompany activity has been eliminated.

Funding Sources

Our device leasing and installment billing programs require a greater use of operating cash flows in the earlier part of the device contracts as our subscribers will generally pay less upfront than a traditional subsidy program. The Accounts Receivable Facility and the Handset Sale-Leaseback transactions described below were designed in large part to mitigate the significant use of cash from purchasing devices from OEMs to fulfill our installment billing and leasing programs. We entered into the Network Equipment Sale-Leaseback transaction in April 2016 to sell and leaseback certain network equipment to unrelated bankruptcy-remote SPEs that provided $2.2 billion in cash proceeds. In October 2016, we entered into a spectrum financing transaction whereby a portion of our spectrum holdings was used as collateral to issue $3.5 billion in senior secured notes. In February 2017, we entered into a new credit agreement for $6.0 billion, consisting of a $4.0 billion, seven-year secured term loan that matures in February 2024 and a $2.0 billion secured revolving bank credit facility that expires in February 2021.

Accounts Receivable Facility

Transaction Overview

Our Accounts Receivable Facility (Receivables Facility) provides us the opportunity to sell certain wireless service receivables, installment receivables, and future amounts due from customers who lease certain devices from us to unaffiliated third parties (the Purchasers). The maximum funding limit under the Receivables Facility is $4.3 billion. While we have the right to decide how much cash to receive from each sale, the maximum amount of cash available to us varies based on a number of factors and currently represents approximately 50% of the total amount of the eligible receivables sold to the Purchasers. As of March 31, 2017, the total amount available to be drawn was $826 million. The Receivables Facility was amended in November 2016 to, among other things, reallocate the Purchasers' commitments between wireless service, installment and future lease receivables to 33%, 39% and 28%, respectively. The amendment was in response to changing trends in the financing methods selected by customers. In February 2017, the Receivables Facility was amended to extend the maturity date to November 2018. Additionally, Sprint gained effective control over the receivables transferred to the Purchasers by obtaining the right, under certain circumstances, to repurchase them. Subsequent to the February 2017 amendment, all proceeds received from the Purchasers in exchange for the transfer of our wireless service and installment receivables are recorded as borrowings and all cash inflows and outflows under the Receivables Facility are reported as financing activities in the consolidated statements of cash flows. As a result of the amendment, there was a non-cash derecognition of the deferred purchase price receivable (DPP) asset totaling $1.5 billion, along with corresponding increases to "Accounts and notes receivable, net" of $2.6 billion, "Other assets" of $563 million and "Long-term debt, financing and capital lease obligations" of $1.7 billion. During the year ended March 31, 2017 and subsequent to the February 2017 amendment, we elected to receive $100 million of cash and also remitted $161 million of funds to the Purchasers because the amount of cash proceeds received by us under the facility exceeded the maximum funding limit, which were reported as financing activities in the consolidated statements of cash flows.

Prior to the February 2017 amendment, wireless service and installment receivables sold to the Purchasers were treated as a sale of financial assets and we derecognized these receivables, as well as the related allowances, and recognized the net proceeds received in cash provided by operating activities in the consolidated statements of cash flows. The total proceeds from the sale of these receivables were comprised of a combination of cash and a DPP. The DPP was realized by us upon either the ultimate collection of the underlying receivables sold to the Purchasers or upon Sprint's election to receive additional advances in cash from the Purchasers subject to the total availability under the Receivables Facility. The fees associated with these sales were recognized in "Selling, general and administrative" in the consolidated statements of operations through the date of the February 2017 amendment. Subsequent to the February 2017 amendment, the sale of wireless service and installment receivables are reported as financings, which is consistent with our historical treatment for the sale of future lease receivables, and the associated fees are recognized as "Interest expense" in the consolidated statements of operations.

Transaction Structure

Sprint contributes certain wireless service, installment and future lease receivables as well as the associated leased devices to Sprint's wholly-owned consolidated bankruptcy-remote SPEs. At Sprint's direction, the SPEs have sold, and will continue to sell, wireless service, installment and future lease receivables to Purchasers or to a bank agent on behalf of the Purchasers. Leased devices will remain with the SPEs, once sales are initiated, and continue to be depreciated over their estimated useful life. At March 31, 2017, wireless service and installment receivables contributed to the SPEs and included in "Accounts and notes receivable, net" in the consolidated balance sheets were $2.9 billion and the long-term portion of installment receivables included in "Other assets" in the consolidated balance sheets was $569 million. As of March 31, 2017, the net book value of devices contributed to the SPEs was approximately $3.1 billion.

Each SPE is a separate legal entity with its own separate creditors who will be entitled, prior to and upon the liquidation of the SPE, to be satisfied out of the SPE’s assets prior to any assets in the SPE becoming available to Sprint. Accordingly, the assets of the SPE are not available to pay creditors of Sprint or any of its affiliates (other than any other SPE), although collections from these receivables in excess of amounts required to repay the advances, yield and fees of the Purchasers and other creditors of the SPEs may be remitted to Sprint during and after the term of the Receivables Facility.

Sales of eligible receivables by the SPEs generally occur daily and are settled on a monthly basis. Sprint pays a fee for the drawn and undrawn portions of the Receivables Facility. A subsidiary of Sprint services the receivables in exchange for a monthly servicing fee, and Sprint guarantees the performance of the servicing obligations under the Receivables Facility.

DPP

Prior to the February 2017 amendment, the DPP was classified as a trading security within "Prepaid expenses and other current assets" in the consolidated balance sheets and was recorded at its estimated fair value. Subsequent to the February 2017 amendment, the Receivables Facility is accounted for as a financing and therefore the DPP is no longer recorded as a separate asset. The DPP related to our wireless service and installment receivables was $1.2 billion as of March 31, 2016. The fair value of the DPP was estimated using a discounted cash flow model, which relies principally on unobservable inputs such as the nature and credit class of the sold receivables and subscriber payment history, and, for installment receivables sold, the estimated timing of upgrades and upgrade payment amounts for those with upgrade options. Changes in the fair value of the DPP did not have a material impact on our consolidated statements of operations for the years ended March 31, 2017 and 2016.

During the year ended March 31, 2017, prior to the February 2017 amendment, we remitted $270 million of funds to the Purchasers because the amount of cash proceeds received by us under the facility exceeded the maximum funding limit, which increased the total amount of the DPP due to Sprint. We also elected to receive $625 million of cash, which decreased the total amount of the DPP due to Sprint. In addition, during the year ended March 31, 2017, prior to the February 2017 amendment, sales of new receivables exceeded cash collections on previously sold receivables such that the DPP increased by $644 million.

Variable Interest Entity

Sprint determined that certain of the Purchasers, which are multi-seller asset-backed commercial paper conduits (Conduits) are considered variable interest entities because they lack sufficient equity to finance their activities. Sprint's interest in the receivables purchased by the Conduits is not considered a variable interest because it is in assets that represent less than 50% of the total activity of the Conduits.

Handset Sale-Leasebacks

In December 2015 and May 2016, we sold certain iPhone^® devices being leased by our customers to Mobile Leasing Solutions, LLC (MLS), a company formed by a group of equity investors, including SoftBank Group Corp. (SoftBank), and then subsequently leased the devices back. Under the agreements, Sprint generally maintains the customer leases, continues to collect and record lease revenue from the customer and remits monthly rental payments to MLS during the leaseback periods.

Under the agreements, Sprint contributed the devices and the associated customer leases to wholly-owned consolidated bankruptcy-remote special purpose entities of Sprint (SPE Lessees). The SPE Lessees then sold the devices and transferred certain specified customer lease end rights and obligations, such as the right to receive the proceeds from customers who elect to purchase the device at the end of the customer lease term, to MLS in exchange for a combination of cash and DPP. Settlement for the DPP occurs near the end of the agreement and can be reduced to the extent that MLS experiences a loss on the device (either not returned or sold at an amount less than the expected residual value of the device), but only to the extent of the device's DPP balance. In the event that MLS sells the devices returned from our customers at a price greater than the expected device residual value, Sprint has the potential to share some of the excess proceeds.

The SPE Lessees retain all rights to the underlying customer leases, such as the right to receive the rental payments during the device leaseback period, other than the aforementioned certain specified customer lease end rights. Each SPE Lessee is a separate legal entity with its own separate creditors who will be entitled, prior to and upon the liquidation of the SPE Lessee, to be satisfied out of the SPE Lessee’s assets prior to any assets in the SPE Lessee becoming available to Sprint. Accordingly, the assets of the SPE Lessee are not available to pay creditors of Sprint or any of its affiliates. The SPE Lessees are obligated to pay the full monthly rental payments under each device lease to MLS regardless of whether our customers make lease payments on the devices leased to them or whether the customer lease is canceled. Sprint has guaranteed to MLS the performance of the agreements and undertakings of the SPE Lessees under the transaction documents.

Handset Sale-Leaseback Tranche 1 (Tranche 1)

In December 2015, Sprint transferred devices with a net book value of approximately $1.3 billion to MLS in exchange for proceeds totaling $1.1 billion and a DPP of $126 million. We recorded the sale, removed the device from our balance sheet, and classified the leasebacks as operating leases. The difference between the fair value and the net book value of the devices sold was recognized as a loss on disposal of property, plant and equipment in the amount of $65 million and was included in "Other, net" in the consolidated statements of operations for the year ended March 31, 2016. The cash proceeds received in the transaction were reflected as cash provided by investing activities in the consolidated statements of cash flows and payments made to MLS under the leaseback are reflected as "Cost of products" in the consolidated statements of operations. Rent expense related to MLS totaled $494 million and $277 million during the years ended March 31, 2017 and 2016, respectively, and is reflected within cash flows from operations. In December 2016, Sprint terminated Tranche 1 by repurchasing the devices and related customer lease end rights and obligations from MLS for consideration of $375 million of net cash payments and the DPP of $126 million. As a result of the transaction, Sprint recorded $477 million of property, plant and equipment, $16 million of other assets, and was released from certain liabilities. Additionally, the leaseback was canceled and there will be no future rental payments owed to MLS related to Tranche 1. The impact to the consolidated statements of operations as a result of the termination was immaterial.

Handset Sale-Leaseback Tranche 2 (Tranche 2)

In May 2016, Sprint transferred devices with a net book value of approximately $1.3 billion to MLS in exchange for cash proceeds totaling $1.1 billion and a DPP of $186 million. Unlike Tranche 1, Tranche 2 was accounted for as a financing. Accordingly, the devices remain in "Property, plant and equipment, net" in the consolidated balance sheets and we continue to depreciate the assets to their estimated residual values over the respective customer lease terms. At March 31, 2017, the net book value of devices transferred to MLS was approximately $575 million.

The proceeds received are reflected as cash provided by financing activities in the consolidated statements of cash flows and payments made to MLS will be reflected as principal repayments and interest expense. We have elected to account for the financing obligation at fair value. Accordingly, changes in the fair value of the financing obligation are recognized in "Other (expense) income, net" in the consolidated statements of operations over the course of the arrangement.

Tranche 2 primarily includes devices from our iPhone Forever Program, whereas these devices were specifically excluded from Tranche 1. The iPhone Forever Program provides our leasing customers the ability to upgrade their devices and to enter into a new lease agreement, subject to certain conditions, upon Apple's release of a next generation device. Upon a customer exercising their iPhone Forever upgrade right, Sprint has the option to terminate the existing leaseback by immediately remitting all unpaid device leaseback payments and returning the device to MLS. Alternatively, Sprint has the option to transfer the title in the new device to MLS in exchange for the title in the original device (Exchange Option). If Sprint elects the Exchange Option, we are required to continue to pay existing device leaseback rental related to the original device, among other requirements.

To address the introduction of the upgrade feature into the sale-leaseback structure, among other factors, numerous contractual terms from Tranche 1 were modified, which shifted certain risks of ownership in the devices away from MLS to Sprint and resulted in Tranche 2 being accounted for as a financing. For instance, the device leaseback periods are generally longer in Tranche 2 as compared to Tranche 1, and the resulting amounts committed to be paid by the Company represent the initial proceeds received from MLS plus interest. This mitigates MLS's exposure to certain risks for non-returned and damaged devices, as well as to declines in device residual values.

Network Equipment Sale-Leaseback

In April 2016, Sprint sold and leased back certain network equipment to unrelated bankruptcy-remote special purpose entities (collectively, "Network LeaseCo"). The network equipment was used as collateral to raise approximately $2.2 billion in borrowings from external investors, including SoftBank. Sprint's payments to Network LeaseCo during the leaseback period are used by Network LeaseCo to service debt.

Network LeaseCo is a variable interest entity for which Sprint is the primary beneficiary. As a result, Sprint is required to consolidate Network LeaseCo and our consolidated financial statements include Network LeaseCo's debt and the related financing cash inflows. The network assets included in the transaction, which had a net book value of approximately $3.0 billion and consisted primarily of equipment located at cell towers, remain on Sprint's consolidated financial statements and continue to be depreciated over their respective estimated useful lives. At March 31, 2017, these network assets had a net book value of approximately $2.4 billion.

The proceeds received were reflected as cash provided by financing activities in the consolidated statements of cash flows and payments made by Network LeaseCo are reflected as principal repayments and interest expense over the respective terms. Sprint has the option to purchase the equipment at the end of the leaseback term for a nominal amount. All intercompany transactions between Network LeaseCo and Sprint are eliminated in our consolidated financial statements. Principal and interest payments on the borrowings from the external investors will be repaid in staggered, unequal payments through January 2018. The first principal payment of $300 million was made in March 2017 with the remaining $1.9 billion of principal payments due in fiscal year 2017.

Spectrum Financing

In October 2016, Sprint transferred certain directly held and third-party leased spectrum licenses (collectively, "Spectrum Portfolio") to wholly-owned bankruptcy-remote special purpose entities (collectively, "Spectrum Financing SPEs"). The Spectrum Portfolio, which represents approximately 14% of Sprint's total spectrum holdings on a MHz-pops basis, was used as collateral to raise an initial $3.5 billion in senior secured notes at 3.36% per annum from external investors under a $7.0 billion program. Sprint can utilize this financing structure to potentially raise up to an additional $3.5 billion, subject to certain conditions. The notes will be repaid over a five-year term, with interest-only payments over the first four quarters and amortizing quarterly principal payments thereafter commencing in December 2017 through September 2021.

Sprint Communications, Inc. simultaneously entered into a long-term lease with the Spectrum Financing SPEs for the ongoing use of the Spectrum Portfolio. Sprint Communications, Inc. is required to make monthly lease payments to the Spectrum Financing SPEs at a market rate. Those lease payments are sufficient to service the senior secured notes. As the Spectrum Financing SPEs are wholly-owned Sprint subsidiaries, these entities are consolidated and all intercompany activity has been eliminated.