Income from Continuing Operations Per Common Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013
Basic income from continuing operations per common share:
Income from continuing operations	$ 810	$ 887	$ 921
Less: Income from continuing operations allocable to participating securities	(8)	(9)	(11)
Income from continuing operations allocable to common shares	802	878	910
Weighted average common shares outstanding	439	446	456
Basic income from continuing operations per common share (in dollars per share)	$ 1.83	$ 1.97	$ 2.00
Diluted income from continuing operations per common share:
Income from continuing operations	810	887	921
Less: Income from continuing operations allocable to participating securities	(8)	(9)	(11)
Income from continuing operations allocable to common shares	$ 802	$ 878	$ 910
Weighted average shares outstanding and common share equivalents:
Weighted average common shares outstanding	439	446	456
Weighted average effect of share-based payment awards	2	2	1
Denominator in calculation of diluted income per share	441	448	457
Diluted income from continuing operations per common share (in dollars per share)	$ 1.82	$ 1.96	$ 1.99
Income from continuing operations per common share, Other disclosures [Abstract]
Number of anti-dilutive restricted stock awards and options excluded from calculation	1	2	4
Weighted average restricted stock awards considered participating securities	4	5	5

Income from continuing operations allocable to common shares basic.

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Income from continuing operations allocable to common shares diluted.

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Weighted average restricted stock awards considered participating securities.

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Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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Amount of income (loss) from continuing operations attributable to the parent. Also defined as revenue less expenses and taxes from ongoing operations before extraordinary items but after deduction of those portions of income or loss from continuing operations that are allocable to noncontrolling interests.

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The amount of net income (loss) from continuing operations per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) derived from continuing operations during the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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Amount of undistributed earnings (loss) allocated to participating securities for the basic earnings (loss) per share or per unit calculation under the two-class method.

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Amount of undistributed earnings (loss) allocated to participating securities for the diluted earnings (loss) per share or per unit calculation under the two-class method.

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

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