Per Share Data (Narrative) (Details) - $ / shares shares in Millions	3 Months Ended	9 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2017
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Class of Warrant or Right, Unissued				62
Class of Warrant or Right, Number of Securities Called by Warrants or Rights				55
Class of Warrant or Right, Exercise Price of Warrants or Rights	$ 5.25	$ 5.25
Options and RSUs [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount			118
Options and Restricted Stock Units [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	47	61
Warrant [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	13	21
Warrant [Member] | SoftBank [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	9	17
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