Intangible Assets (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	9 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Feb. 01, 2018
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Goodwill, Period Increase (Decrease)	$ 7
Share Price	$ 5.89
Net book value per share price	$ 6.56
Other, Net [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Gain (Loss) on Disposition of Intangible Assets	$ 479	$ 354
Subsequent Event [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Share Price			$ 5.36
Corporate Joint Venture [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Preferred economic interest (as a percent)	68.00%
Common voting interest (as a percent)	55.00%
Beginning assets joint venture	$ 390
Beginning liabilities joint venture	240
Fair value of joint venture assets	270
Fair value of joint venture liabilities	220
Current and fixed assets of joint venture	85
Acquired long term debt	170
Acquired other current liabilities	$ 50
Corporate Joint Venture [Member] | PRWireless PR, Inc. [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Preferred economic interest (as a percent)	32.00%
Common voting interest (as a percent)	45.00%
Corporate Joint Venture [Member] | Other Intangible Assets [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Intangible assets acquired	$ 35
Corporate Joint Venture [Member] | FCC Licenses [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Intangible assets acquired	$ 150