Income from Continuing Operations Per Common Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2011	Dec. 31, 2010
Basic income from continuing operations per common share:
Income from continuing operations	$ 263	$ 196	$ 727	$ 636
Income from continuing operations allocable to common shares	260	194	718	629
Weighted-average common shares outstanding	483	505	492	507
Basic income from continuing operations per common share	$ 0.54	$ 0.38	$ 1.46	$ 1.24
Diluted income from continuing operations per common share:
Income from continuing operations	263	196	727	636
Income from continuing operations allocable to common shares	260	194	718	629
Weighted average shares outstanding and common share equivalents:
Weighted-average common shares outstanding	483	505	492	507
Weighted average effect of share-based payment awards	1	1	1	1
Denominator in calculation of diluted income per share	484	506	493	508
Diluted income from continuing operations per common share	$ 0.54	$ 0.38	$ 1.46	$ 1.24
Income Per Common Share (Textual) [Abstract]
Number of anti-dilutive restricted stock awards and options excluded from the calculation	6	5	6	8
Weighted average restricted stock awards considered participating securities	6	6	6	6
Basic [Member]
Reconciliation of earnings per common share [Line Items]
Less: Income from continuing operations allocable to participating securities	(3)	(2)	(9)	(7)
Diluted [Member]
Reconciliation of earnings per common share [Line Items]
Less: Income from continuing operations allocable to participating securities	$ (3)	$ (2)	$ (9)	$ (7)