Earnings Per Common Share (Basic and Diluted Earnings per Common Share) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended				9 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2013		Dec. 31, 2012
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Income from continuing operations	$ 156		$ 306		$ 992		$ 1,084
Loss from discontinued operations, net of tax	(92)		(8)		(100)		(5)
Net income	$ 64		$ 298		$ 892		$ 1,079
Weighted average common shares outstanding:
Basic	230		235		229		236
Effect of dilutive securities:
Diluted	234		240		233		240
Diluted
Continuing operations	$ 0.67	[1]	$ 1.27	[1]	$ 4.26	[1]	$ 4.51	[1]
Discontinued operations	$ (0.39)	[1]	$ (0.03)	[1]	$ (0.43)	[1]	$ (0.02)	[1]
Total	$ 0.28	[1]	$ 1.24	[1]	$ 3.83	[1]	$ 4.49	[1]
Basic
Continuing operations	$ 0.68	[1]	$ 1.30	[1]	$ 4.34	[1]	$ 4.60	[1]
Discontinued operations	$ (0.40)	[1]	$ (0.03)	[1]	$ (0.44)	[1]	$ (0.02)	[1]
Total	$ 0.28	[1]	$ 1.27	[1]	$ 3.90	[1]	$ 4.58	[1]
Options to purchase common stock [Member]
Effect of dilutive securities:
Dilutive securities	2		1		1		1
Restricted Stock Units [Member]
Effect of dilutive securities:
Dilutive securities	2		4		3		3

[1] Certain computations may reflect rounding adjustments.