Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2017
Income Tax Disclosure [Abstract]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			31.50%
Provisional estimate non-cash tax benefit			$ 7,100
Non-cash tax benefit remeasurement of deferred tax assets			5,000
Non-cash tax benefit reduction of valuation allowance			2,100
Income Tax Reconciliation, Change in Deferred Tax Assets Valuation Allowance			64	$ 522
Income tax benefit	$ (7,052)	$ 111	(6,662)	286
Tax benefit from organizational restructuring			0	42
Temporary differences between carrying amounts of FCC licenses for financial statement purposes and their tax bases			0	46
Increase deferred tax liability for business activity changes			69	0
Unrecognized tax benefit	$ 191		191		$ 190
Income Taxes Paid, Net			$ 55	$ 34