Quarterly Financial And Market Information (Summary Of Quarterly Financial And Market Information) (Details) - USD ($) $ / shares in Units, $ 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
Quarterly Financial And Market Information [Line Items]
Net revenue	$ 1,527		$ 1,149	$ 898	$ 1,271	$ 1,308	$ 1,070	$ 815	$ 1,203	$ 4,845	$ 4,396	$ 4,515
Gross profit	1,325		633	497	1,092	1,082	524	406	1,030	3,547	3,042	3,086
Operating income (loss)	717		(4)	(49)	560	536	(31)	(119)	512	1,224	898	948
Net income (loss)	$ 566	[1]	$ (1)	$ (38)	$ 440	$ 899	$ (45)	$ (140)	$ 442	$ 967	$ 1,156	$ 875
Earnings per share - Basic	$ 1.84		$ 0.00	$ (0.13)	$ 1.46	$ 2.93	$ (0.14)	$ (0.45)	$ 1.42	$ 3.19	$ 3.73	$ 2.81
Earnings per share - Diluted	1.81		0.00	(0.13)	1.40	2.79	(0.14)	(0.45)	1.32	3.08	3.50	$ 2.69
High price, Common stock per share	91.51		85.56	85.40	77.25	70.83	76.77	75.16	68.00	91.51	76.77
Low price, Common stock per share	$ 78.64		$ 75.58	$ 75.38	$ 61.85	$ 55.50	$ 65.04	$ 63.43	$ 56.03	$ 61.85	$ 55.50

[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.