Retirement Benefit Liabilities - Summary of retirement benefits (Details) - USD ($) $ in Millions	Dec. 31, 2016	Sep. 30, 2016
Compensation and Retirement Disclosure [Abstract]
Retiree medical liability	$ 442	$ 447
Pension liability	274	283
Other	14	13
Subtotal	730	743
Less: current portion (included in compensation and benefits, Note 16)	(39)	(40)
Retirement benefits	$ 691	$ 703

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This represents the entire liability recognized in the balance sheet that is associated with the defined benefit pension plans.

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The total amount of the entity's obligation as of the balance sheet date under any other retirement plan(s), such as one or more defined contribution plans.

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This represents the entire liability recognized in the balance sheet that is associated with other postretirement defined benefit plans (excluding pension plans).

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For a classified balance sheet, the amount recognized in balance sheet as a current liability associated with an underfunded defined benefit plan.

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This represents the entire liability recognized in the balance sheet that is associated with the defined benefit plans.

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This represents the noncurrent liability for underfunded plans recognized in the balance sheet that is associated with the defined benefit pension plans and other postretirement defined benefit plans.

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