Earnings Per Share - Earnings Per Share (Detail) - USD ($) shares in Millions, $ in Millions	3 Months Ended	6 Months Ended
Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share [Abstract]
Income (loss) from continuing operations	$ 438	$ (148)	$ 668	$ 224
Loss from discontinued operations	0	0	0	(43)
Basic and diluted income (loss) available to shareholders	$ 438	$ (148)	$ 668	$ 181
Weighted Average Shares Outstanding
Basic weighted average shares outstanding	926.2	939.2	926.2	938.2
Effect of dilutive securities:
Stock options, unvested restricted stock and unvested performance share awards	6.3	0.0	6.7	9.8
Diluted weighted average shares outstanding	932.5	939.2	932.9	948.0
Antidilutive Securities
Options to purchase shares	1.4	0.0	1.2	0.1

Antidilutive securities.

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Effect Of Dilutive Securities [Abstract]

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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 after tax of income (loss) from continuing operations attributable to the parent.

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Amount after tax of income (loss) from a discontinued operation attributable to the parent. Includes, but is not limited to, the income (loss) from operations during the phase-out period, gain (loss) on disposal, gain (loss) for reversal of write-down (write-down) to fair value, less cost to sell, and adjustments to a prior period gain (loss) on disposal.

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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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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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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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