Stockholders' Equity and Per Share Data (Narrative) (Details) - USD ($)		3 Months Ended								12 Months Ended
	Jul. 10, 2018	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017	Apr. 01, 2018
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax		$ (392,000,000)				$ (313,000,000)				$ (392,000,000)	$ (313,000,000)		$ (321,000,000)
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest										$ (1,943,000,000)	$ 7,377,000,000	$ (1,206,000,000)
Capital stock authorized (in shares)		10,020,000,000								10,020,000,000
Common shares, shares authorized (in shares)		9,000,000,000				9,000,000,000				9,000,000,000	9,000,000,000
Common stock, par value		$ 0.01				$ 0.01				$ 0.01	$ 0.01
Preferred stock, shares authorized (in shares)		20,000,000								20,000,000
Preferred stock, par value		$ 0.0001								$ 0.0001
Common stock, shares, outstanding (in shares)		4,100,000,000								4,100,000,000
Net Income (Loss) Attributable to Noncontrolling Interest										$ 0	$ (12,000,000)	0
Net Income (Loss) Attributable to Parent		$ (2,174)	$ (141)	$ 196	$ 176	$ 0	$ 0	$ 0	$ 0	$ (1,943,000,000)	$ 7,389,000,000	$ (1,206,000,000)
Weighted Average Number of Shares Outstanding, Basic										4,057,000,000	3,999,000,000	3,981,000,000
Weighted Average Number of Shares Outstanding, Diluted										4,057,000,000	4,078,000,000	3,981,000,000
Earnings Per Share, Basic		$ (0.53)	$ (0.03)	$ 0.05	$ 0.04	$ 0.02	$ 1.79	$ (0.01)	$ 0.05	$ (0.48)	$ 1.85	$ (0.30)
Earnings Per Share, Diluted		$ (530,000)	$ (30,000)	$ 50,000	$ 40,000	$ 20,000	$ 1,760,000	$ (10,000)	$ 50,000	$ (0.48)	$ 1.81	$ (0.30)
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								9,000,000,000
Common stock, par value		$ 0.01								$ 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								1,000,000,000
Common stock, par value		$ 0.01								$ 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)						6,000,000					6,000,000
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
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
Proceeds from Warrant Exercises	$ 287,000,000
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										92,000,000
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
Retained Earnings [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net Income (Loss) Attributable to Parent										$ (1,943,000,000)	$ 7,389,000,000