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
	Jun. 30, 2013		Jun. 30, 2012
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Income from continuing operations	$ 420		$ 379
Income from discontinued operations, net of tax	4		1
Net income	$ 424		$ 380
Weighted average common shares outstanding:
Basic	227		236
Effect of dilutive securities:
Diluted	232		240
Diluted
Continuing operations	$ 1.81	[1]	$ 1.58	[1]
Discontinued operations	$ 0.02	[1]	$ 0.00	[1]
Total	$ 1.83	[1]	$ 1.58	[1]
Basic
Continuing operations	$ 1.84	[1]	$ 1.61	[1]
Discontinued operations	$ 0.02	[1]	$ 0.00	[1]
Total	$ 1.86	[1]	$ 1.61	[1]
Options to purchase common stock [Member]
Effect of dilutive securities:
Dilutive securities	2		1
Restricted Stock Units [Member]
Effect of dilutive securities:
Dilutive securities	3		3

[1] Certain computations may reflect rounding adjustments.