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				6 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Income from continuing operations	$ 416		$ 399		$ 836		$ 778
Income (loss) from discontinued operations, net of tax	(12)		2		(8)		3
Net income	$ 404		$ 401		$ 828		$ 781
Weighted average common shares outstanding:
Basic	229		236		228		236
Effect of dilutive securities:
Diluted	233		240		232		240
Diluted
Continuing operations	$ 1.79	[1]	$ 1.66	[1]	$ 3.60	[1]	$ 3.24	[1]
Discontinued operations	$ (0.05)	[1]	$ 0.01	[1]	$ (0.04)	[1]	$ 0.01	[1]
Total	$ 1.74	[1]	$ 1.67	[1]	$ 3.56	[1]	$ 3.25	[1]
Basic
Continuing operations	$ 1.82	[1]	$ 1.69	[1]	$ 3.67	[1]	$ 3.30	[1]
Discontinued operations	$ (0.06)	[1]	$ 0.01	[1]	$ (0.04)	[1]	$ 0.01	[1]
Total	$ 1.76	[1]	$ 1.70	[1]	$ 3.63	[1]	$ 3.31	[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		3		3		3

[1] Certain computations may reflect rounding adjustments.