Supplemental Financial Information (Details) - USD ($) $ in Millions	Mar. 31, 2018	Mar. 31, 2017
Accounts and notes receivable, net
Trade	$ 2,916	$ 2,947
Unbilled trade and other	1,204	1,545
Less allowance for doubtful accounts	(409)	(354)
Accounts and notes receivable, net	3,711	4,138
Prepaid expenses and other current assets
Prepaid expenses	263	298
Restricted Cash, Current	0	21
Deferred charges and other	312	282
Prepaid expense and other assets, current	575	601
Other assets
Unbilled trade installment receivables, net	154	569
Investments	197	237
Restricted Cash, Noncurrent	49	51
Other	521	456
Other assets	921	1,313
Accounts payable
Trade	3,068	2,937
Accrued interconnection costs	80	123
Capital expenditures and other	261	221
Accounts payable	3,409	3,281
Accrued expenses and other current liabilities
Deferred revenues	1,454	1,445
Accrued interest	423	511
Accrued taxes	410	435
Payroll and related	405	339
Accrued legal reserves	194	296
Severance, lease and other exit costs	108	83
Asset Retirement Obligation, Current	145	157
Unfavorable lease liabilities	152	168
Other	671	707
Accrued expenses and other current liabilites	3,962	4,141
Other liabilities
Deferred rental income-communications towers	199	207
Deferred rent	605	554
Asset retirement obligations	486	462
Unfavorable lease liabilities	337	490
Post-retirement benefits and other non-current employee related liabilities	833	861
Deferred spectrum lease liability	416	348
Other liabilities	607	641
Other Liabilities	3,483	3,563
Checks issued in excess of associated bank balances but not yet presented for collection	$ 66	$ 69