Related Party Transactions (Brightstar) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Mar. 31, 2019
Related Party Transaction [Line Items]
Total revenue	$ 7,795	$ 8,433	$ 15,937	$ 16,558
Cost of equipment sales	1,359	1,517	2,700	2,787
Brightstar [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	14	16	27	33
Related Party Transaction, Other Revenues from Transactions with Related Party	42	48	84	97
Accounts Receivable, Related Parties	211		211		$ 187
Accounts Payable, Related Parties, Current	78		78		$ 109
Total revenue	352	414	696	829
Cost of equipment sales	$ 382	$ 434	$ 743	$ 866

Cost of equipment sales

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Amount for accounts payable to related parties. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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For an unclassified balance sheet, amount of receivables arising from transactions with related parties.

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Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Reflects the sum of all other revenue and income realized from sales and other transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party during the period.

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No definition available.

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Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

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