Income from Continuing Operations Per Common Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Jun. 30, 2012	Jun. 30, 2011
Basic income from continuing operations per common share:
Income from continuing operations	$ 240	$ 228
Less: Income from continuing operations allocable to participating securities	237	225
Weighted-average common shares outstanding	465	500
Basic income from continuing operations per common share	$ 0.51	$ 0.45
Diluted income from continuing operations per common share:
Income from continuing operations	240	228
Income from continuing operations allocable to common shares	237	225
Weighted average shares outstanding and common share equivalents:
Weighted-average common shares outstanding	465	500
Weighted average effect of share-based payment awards	2	1
Denominator in calculation of diluted income per share	467	501
Diluted income from continuing operations per common share	$ 0.51	$ 0.45
Income Per Common Share (Textual) [Abstract]
Number of anti-dilutive restricted stock awards and options excluded from the calculation	3	5
Weighted average restricted stock awards considered participating securities	6	7
Basic [Member]
Reconciliation of earnings per common share [Line Items]
Less: Income from continuing operations allocable to participating securities	(3)	(3)
Diluted [Member]
Reconciliation of earnings per common share [Line Items]
Less: Income from continuing operations allocable to participating securities	$ (3)	$ (3)