Income Taxes Income Taxes (Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2017	Mar. 31, 2017
Deferred tax assets
Net operating loss carryforwards	$ 4,169	$ 6,812
Tax credit carryforwards	365	340
Capital loss carryforwards	0	1
Property, plant and equipment	1,997	2,192
Debt obligations	83	205
Deferred rent	237	402
Pension and other postretirement benefits	211	332
Accruals and other liabilities	907	1,454
Deferred tax assets, gross, noncurrent	7,969	11,738
Valuation allowance	(5,212)	(10,477)
Deferred tax assets, net of valuation allowance, noncurrent	2,757	1,261
Deferred tax liabilities
FCC licenses	8,793	12,876
Trademarks	1,122	1,712
Intangibles	340	771
Other	211	318
Deferred tax liabilities, long-term	10,466	15,677
Long-term deferred tax liability	$ 7,709	$ 14,416