Stockholders' Equity and Per Share Data (Narrative) (Details) - $ / shares	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Capital stock authorized (in shares)	10,020,000,000
Common shares, shares authorized (in shares)	9,000,000,000	9,000,000,000
Common stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized (in shares)	20,000,000
Preferred stock, par value	$ 0.0001
Common stock, shares, outstanding (in shares)	4,000,000,000
Class of Warrant or Right, Unissued	62,000,000
Number of stock that will be issued shares warrant (in shares)	55,000,000
Class of warrant or right, exercise price of warrants or rights	$ 5.25
Series 1 Voting [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Common shares, shares authorized (in shares)	9,000,000,000
Common stock, par value	$ 0.01
Non Voting [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Common shares, shares authorized (in shares)	1,000,000,000
Common stock, par value	$ 0.01
Options and RSUs [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Number of shares that had no effect on computation of dilutive weighted average number of shares outstanding (in shares)		114,000,000	73,000,000
Options and Restricted Stock Units [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Incremental Common Shares Attributable to Dilutive Effect of Equity Unit Purchase Agreements	61,000,000
Warrant [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Incremental Common Shares Attributable to Dilutive Effect of Equity Unit Purchase Agreements	18,000,000
Employee Stock Option [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	6,000,000
SoftBank [Member] | Warrant [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Incremental Common Shares Attributable to Dilutive Effect of Equity Unit Purchase Agreements	14,000,000