Retirement Benefit Liabilities - Summary of retirement benefits (Details) - USD ($) $ in Millions	Jun. 30, 2017	Sep. 30, 2016
Retirement Benefits [Abstract]
Retiree medical liability	$ 432	$ 447
Pension liability	261	283
Other	13	13
Subtotal	706	743
Less: current portion (included in compensation and benefits, Note 15)	(39)	(40)
Retirement benefits	$ 667	$ 703

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Amount of liability, recognized in statement of financial position, for defined benefit pension plan. Excludes other postretirement benefit plan.

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Amount of liability for retirement benefits, classified as other.

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