Income Taxes (Deferred Income Tax Assets and Liabilities) (Details) - USD ($) $ in Millions	Mar. 31, 2017	Mar. 31, 2016
Deferred tax assets
Net operating loss carryforwards, long-term	$ 6,812	$ 8,057
Tax credit carryforwards, long-term	340	384
Capital loss carryforwards, long-term	1	83
Property, plant and equipment, long-term	2,192	1,230
Debt obligations, long-term	205	0
Deferred rent, long-term	402	438
Pension and other postretirement benefits, long-term	332	378
Accruals and other liabilities, long-term	1,454	1,376
Deferred tax assets, gross, noncurrent	11,738	11,946
Valuation allowance, noncurrent	(10,477)	(9,793)
Deferred tax assets, net of valuation allowance, noncurrent	1,261	2,153
Deferred tax liabilities
FCC Licenses	12,876	12,738
Trademarks	1,712	1,718
Intangibles	771	1,166
Deferred Tax Liabilities, Deferred Expense, Debt Issuance Costs	0	58
Other, long-term	318	432
Deferred tax liabilities, long-term	15,677	16,112
Long-term deferred tax liability	$ 14,416	$ 13,959