Income Taxes (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Income Tax Contingency [Line Items]
Federal statutory income tax rate	21.00%	31.50%	35.00%
Tax Cuts And Jobs Act Of 2017, Incomplete Accounting, Change In Tax Rate, Deferred Tax Asset, Provisional Income Tax Expense (Benefit)		$ 7,100
Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax (Asset) Liability		5,000
Income Tax Expense (Benefit), Continuing Operations Adjustment, Deferred Tax Asset Valuation Allowance		2,100
Income tax benefit (expense)	$ 35	7,074	$ (435)
Goodwill, Impairment Loss, Net of Tax	1,900
Goodwill, Impairment Loss	2,000
Change in valuation allowance	8	(224)	615
Effective Income Tax Rate Reconciliation, Other Adjustments, Amount	13	0	118
Income (loss) from continuing operations before income taxes, foreign	(61)	(109)	204
Deferred tax assets, operating loss carryforwards, domestic	4,500
Deferred tax assets, operating loss carryforwards, state and local	937
Deferred tax assets, operating loss carryforwards, foreign	145
Deferred tax assets, tax credit carryforwards	356
Unrecognized tax benefit	242	$ 239	190
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	221
Significant change in unrecognized tax benefits is reasonably possible, estimated range of change, upper bound	18
Temporary differences between carrying amounts of FCC licenses for financial statement purposes and their tax bases [Member]
Income Tax Contingency [Line Items]
Income tax benefit (expense)			(136)
Internal Revenue Service (IRS) [Member]
Income Tax Contingency [Line Items]
Operating loss carryforwards	21,300
State and Local Jurisdiction [Member]
Income Tax Contingency [Line Items]
Income tax benefit (expense)			$ (89)
Operating loss carryforwards	16,300
Foreign Tax Authority [Member]
Income Tax Contingency [Line Items]
Operating loss carryforwards	392
Expiration Between 2016 and 2020 [Member]
Income Tax Contingency [Line Items]
Operating loss carryforwards	411
Expiration Between 2021 and 2034 [Member]
Income Tax Contingency [Line Items]
Operating loss carryforwards	13,600
No Expiration [Member]
Income Tax Contingency [Line Items]
Operating loss carryforwards	7,300
Deferred tax assets, tax credit carryforwards	38
No Expiration [Member] | State and Local Jurisdiction [Member]
Income Tax Contingency [Line Items]
Operating loss carryforwards	402
No Expiration [Member] | Foreign Tax Authority [Member]
Income Tax Contingency [Line Items]
Operating loss carryforwards	22
Expire through 2038 [Member] | State and Local Jurisdiction [Member]
Income Tax Contingency [Line Items]
Operating loss carryforwards	15,936
Expire prior to 2018 [Member]
Income Tax Contingency [Line Items]
Deferred tax assets, tax credit carryforwards	22
Expire Between 2016 and 2034 [Member] [Member]
Income Tax Contingency [Line Items]
Deferred tax assets, tax credit carryforwards	$ 296