Income Taxes (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Income Tax Contingency [Line Items]
Federal statutory income tax rate	31.50%
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)	7,074	$ (435)	$ (141)
Change in valuation allowance	(224)	615	939
Effective Income Tax Rate Reconciliation, Other Adjustments, Amount	0	118	(90)
Income (loss) from continuing operations before income taxes, foreign	(109)	204	343
Deferred tax assets, operating loss carryforwards, domestic	2,900
Deferred tax assets, operating loss carryforwards, state and local	952
Deferred tax assets, operating loss carryforwards, foreign	297
Deferred tax assets, capital loss carryforwards	0	1
Deferred tax assets, tax credit carryforwards	353
Unrecognized tax benefit	239	$ 190	$ 166
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	217
Significant change in unrecognized tax benefits is reasonably possible, estimated range of change, upper bound	34
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	13,900
State and Local Jurisdiction [Member]
Income Tax Contingency [Line Items]
Income tax benefit (expense)	(89)
Operating loss carryforwards	16,000
Foreign Tax Authority [Member]
Income Tax Contingency [Line Items]
Operating loss carryforwards	953
Expiration Between 2016 and 2020 [Member]
Income Tax Contingency [Line Items]
Operating loss carryforwards	703
Expiration Between 2021 and 2034 [Member]
Income Tax Contingency [Line Items]
Operating loss carryforwards	13,200
No Expiration [Member]
Income Tax Contingency [Line Items]
Deferred tax assets, tax credit carryforwards	35
No Expiration [Member] | Foreign Tax Authority [Member]
Income Tax Contingency [Line Items]
Operating loss carryforwards	550
Expire prior to 2018 [Member]
Income Tax Contingency [Line Items]
Deferred tax assets, tax credit carryforwards	12
Expire Between 2016 and 2034 [Member] [Member]
Income Tax Contingency [Line Items]
Deferred tax assets, tax credit carryforwards	$ 306