Income Taxes (Effective Income Tax Rate) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Income tax benefit at the federal statutory rate			$ (205)	$ 223
State income taxes, net of federal income tax effect			(57)	8
Cumulative effect of changes in corporate state income tax laws that were recognized within State income taxes, net of federal income tax effect			(28)	3
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
Credit for increasing research activities			11	0
Tax benefit from organizational restructuring			0	42
Change in federal and state valuation allowance			(64)	(522)
Increase in liability for unrecognized tax benefits			(20)	0
Tax benefit from the Tax Act			7,090	0
Other, net			4	6
Income tax benefit (expense)	$ 7,052	$ (111)	$ 6,662	$ (286)
Effective income tax rate			1021.80%	44.90%