Computation of Earnings Per Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended	6 Months Ended
Nov. 30, 2014	Nov. 30, 2013	Nov. 30, 2014	Nov. 30, 2013
Basic earnings per common share:
Net earnings allocable to common shares	$ 615	$ 499	$ 1,220	$ 988
Weighted-average common shares	283	315	284	316
Basic earnings per common share	$ 2.17us-gaap_EarningsPerShareBasic	$ 1.58us-gaap_EarningsPerShareBasic	$ 4.30us-gaap_EarningsPerShareBasic	$ 3.13us-gaap_EarningsPerShareBasic
Diluted earnings per common share:
Net earnings allocable to common shares	$ 615	$ 499	$ 1,220	$ 988
Weighted-average common shares	283	315	284	316
Dilutive effect of share-based awards	4	4	4	3
Weighted-average diluted shares	287	319	288	319
Diluted earnings per common share	$ 2.14us-gaap_EarningsPerShareDiluted	$ 1.57us-gaap_EarningsPerShareDiluted	$ 4.24us-gaap_EarningsPerShareDiluted	$ 3.10us-gaap_EarningsPerShareDiluted
Anti-dilutive options excluded from diluted earnings per common share	2.2	2.5	2.2	6.2

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

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The amount of net income (loss) for 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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Net income after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period).

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Net Income or Loss Available to Common Stockholders plus adjustments resulting from the assumption that dilutive convertible securities were converted, options or warrants were exercised, or that other shares were issued upon the satisfaction of certain conditions.

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