Earnings Per Share (Computation Of Basic Earnings And Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended										12 Months Ended
		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
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net income (loss)		$ 209	$ 262	$ 255	$ 293	$ 607	[1]	$ (186)	[1]	$ (22)	$ 644	$ 1,019	$ 1,043	$ 967
Weighted-average common stock outstanding - basic												303	308	303
Dilutive potential common shares related to stock award plans and from assumed exercise of stock options												3	4	4
Dilutive potential common shares related to the Convertible Notes	[2]											0	0	1
Dilutive potential common shares related to the Warrants	[2]											0	0	6
Weighted Average Number of Shares Outstanding, Diluted												306	312	314
Basic		$ 0.70	$ 0.87	$ 0.84	$ 0.96	$ 1.98		$ (0.60)		$ (0.07)	$ 2.08	$ 3.36	$ 3.39	$ 3.19
Diluted		$ 0.69	$ 0.86	$ 0.83	$ 0.95	$ 1.95		$ (0.60)		$ (0.07)	$ 2.06	$ 3.33	$ 3.34	$ 3.08

[1] During the quarters ended December 31, 2017 and March 31, 2018, we recognized tax expense of $176 million and $59 million, respectively, due to the application of the U.S. Tax Act, enacted on December 22, 2017.

[2] See Note 10 — Financing Arrangements in our Annual Report on Form 10-K for the fiscal year ended March 31, 2017, for additional information regarding the potential dilutive shares related to our Convertible Notes and Warrants. The Convertible Notes matured on July 15, 2016 and the Warrants expired on January 12, 2017.