Income Taxes (Deferred Income Tax Assets and Liabilities) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Mar. 31, 2018
Deferred tax assets
Net operating loss carryforwards, long-term	$ 5,478	$ 4,116
Tax credit carryforwards, long-term	241	244
Property, plant and equipment, long-term	900	2,192
Debt obligations, long-term	0	64
Deferred rent, long-term	247	231
Pension and other postretirement benefits, long-term	209	219
Accruals and other liabilities, long-term	791	913
Deferred tax assets, gross, noncurrent	7,866	7,979
Valuation allowance, noncurrent	(4,504)	(4,745)
Deferred tax assets, net of valuation allowance, noncurrent	3,362	3,234
Deferred tax liabilities
FCC Licenses	8,968	8,877
Trademarks	1,129	1,131
Intangibles	147	298
Other, long-term	258	222
Deferred tax liabilities, long-term	10,918	10,528
Long-term deferred tax liability	7,556	7,294
Deferred Tax Liabilities, Deferred Expense	401
Deferred Tax Liabilities, Deferred Expense, Debt Issuance Costs	$ 15	$ 0