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, 2017		Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net income (loss)	$ 566	[1]	$ (1)	$ (38)	$ 440	$ 899	$ (45)	$ (140)	$ 442	$ 967	$ 1,156	$ 875
Weighted-average common stock outstanding - basic										303	310	311
Dilutive potential common shares related to stock award plans and from assumed exercise of stock options										4	6	9
Dilutive potential common shares related to the Convertible Notes										1	6	4
Dilutive potential common shares related to the Warrants										6	8	1
Weighted Average Number of Shares Outstanding, Diluted										314	330	325
Basic	$ 1.84		$ 0.00	$ (0.13)	$ 1.46	$ 2.93	$ (0.14)	$ (0.45)	$ 1.42	$ 3.19	$ 3.73	$ 2.81
Diluted	$ 1.81		$ 0.00	$ (0.13)	$ 1.40	$ 2.79	$ (0.14)	$ (0.45)	$ 1.32	$ 3.08	$ 3.50	$ 2.69

[1] Net income includes an income tax benefit recorded in the fourth quarter of fiscal year 2016 for the reversal of a significant portion of our deferred tax valuation allowance.