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, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net income (loss)	$ 418	$ 346	$ 854	$ 1,421	$ 209	$ 262	$ 255	$ 293	$ 3,039	$ 1,019	$ 1,043
Weighted-average common stock outstanding - basic									293	303	308
Dilutive potential common shares related to stock award plans and from assumed exercise of stock options									2	3	4
Weighted Average Number of Shares Outstanding, Diluted									295	306	312
Basic	$ 1.44	$ 1.18	$ 2.89	$ 4.78	$ 0.70	$ 0.87	$ 0.84	$ 0.96	$ 10.37	$ 3.36	$ 3.39
Diluted	$ 1.43	$ 1.18	$ 2.89	$ 4.75	$ 0.69	$ 0.86	$ 0.83	$ 0.95	$ 10.30	$ 3.33	$ 3.34