Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Mar. 31, 2016
Operating Loss Carryforwards [Line Items]
Income Tax Reconciliation, Change in Deferred Tax Assets Valuation Allowance			$ 522	$ 647
Income tax benefit	$ 111	$ 97	286	126
Unrecognized tax benefit	$ 176		176		$ 166
Income Taxes Paid, Net			34	$ 34
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Income tax benefit			42
Temporary differences between carrying amounts of FCC licenses for financial statement purposes and their tax bases [Member]
Operating Loss Carryforwards [Line Items]
Income tax benefit			$ 46