Income Taxes (Narrative) (Details) - USD ($) $ in Millions		12 Months Ended
		Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Income Tax Contingency [Line Items]
Change in valuation allowance		$ 615	$ 939	$ 911
Income tax expense		435	141	(574)
Effective Income Tax Rate Reconciliation, Other Adjustments, Amount		118	(90)	0
Income (loss) from continuing operations before income taxes, foreign		204	343	398
Deferred tax assets, operating loss carryforwards, domestic		5,700
Deferred tax assets, operating loss carryforwards, state and local		863
Deferred tax assets, operating loss carryforwards, foreign		265
Deferred tax assets, capital loss carryforwards		1	83
Deferred tax assets, tax credit carryforwards		429
Unrecognized tax benefit		190	$ 166	163
Significant change in unrecognized tax benefits is reasonably possible, estimated range of change, upper bound		42
Unrecognized Tax Benefits that Would Impact Effective Tax Rate		175
Temporary differences between carrying amounts of FCC licenses for financial statement purposes and their tax bases [Member]
Income Tax Contingency [Line Items]
Income tax expense		136
Internal Revenue Service (IRS) [Member]
Income Tax Contingency [Line Items]
Operating loss carryforwards		16,400
State and Local Jurisdiction [Member]
Income Tax Contingency [Line Items]
Income tax expense		89
Operating loss carryforwards		17,500
Foreign Tax Authority [Member]
Income Tax Contingency [Line Items]
Operating loss carryforwards		805
Expiration Between 2016 and 2020 [Member]
Income Tax Contingency [Line Items]
Operating loss carryforwards		620
Expiration Between 2021 and 2034 [Member]
Income Tax Contingency [Line Items]
Operating loss carryforwards		15,800
No Expiration [Member]
Income Tax Contingency [Line Items]
Deferred tax assets, tax credit carryforwards		54
No Expiration [Member] | Foreign Tax Authority [Member]
Income Tax Contingency [Line Items]
Operating loss carryforwards		446
Expire prior to 2018 [Member]
Income Tax Contingency [Line Items]
Deferred tax assets, tax credit carryforwards		74
Expire Between 2016 and 2034 [Member] [Member]
Income Tax Contingency [Line Items]
Deferred tax assets, tax credit carryforwards		301
Trademarks [Member]
Income Tax Contingency [Line Items]
Impairment of intangible assets, indefinite-lived (excluding goodwill)	[1]	$ 0
Wireless [Member] | Trademarks [Member]
Income Tax Contingency [Line Items]
Impairment of intangible assets, indefinite-lived (excluding goodwill)				$ 1,900

[1] .