Gross Fair Value of Derivative Positions (Details) - USD ($) $ in Millions	Jun. 30, 2018	Sep. 30, 2017
Current Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	$ 275	$ 219
Derivative Asset, Counterparty Netting Offset	(184)	(142)
Derivative Asset, Collateral, Obligation to Return Cash, Offset	0	(20)
Net derivative positions	91	57
Current Assets | Derivatives designated as hedges | Foreign exchange
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	172	175
Current Assets | Derivatives designated as hedges | Interest rate
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	0	0
Current Assets | Derivatives designated as hedges | Other Derivative
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	11	6
Current Assets | Derivatives not designated as hedges | Foreign exchange
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	92	38
Current Assets | Derivatives not designated as hedges | Interest rate
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	0	0
Other Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	218	202
Derivative Asset, Counterparty Netting Offset	(173)	(190)
Derivative Asset, Collateral, Obligation to Return Cash, Offset	0	(7)
Net derivative positions	45	5
Other Assets | Derivatives designated as hedges | Foreign exchange
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	192	190
Other Assets | Derivatives designated as hedges | Interest rate
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	0	10
Other Assets | Derivatives designated as hedges | Other Derivative
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	3	2
Other Assets | Derivatives not designated as hedges | Foreign exchange
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	23	0
Other Assets | Derivatives not designated as hedges | Interest rate
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	0	0
Other Current Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	(504)	(344)
Derivative Liability, Counterparty netting offset	245	188
Derivative Liability, Collateral, Right to Reclaim Cash, Offset	137	19
Net derivative positions	(122)	(137)
Other Current Liabilities | Derivatives designated as hedges | Foreign exchange
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	(108)	(192)
Other Current Liabilities | Derivatives designated as hedges | Interest rate
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	(297)	(106)
Other Current Liabilities | Derivatives designated as hedges | Other Derivative
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	0	0
Other Current Liabilities | Derivatives not designated as hedges | Foreign exchange
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	(99)	(46)
Other Current Liabilities | Derivatives not designated as hedges | Interest rate
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	0	0
Other Long-Term Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	(177)	(205)
Derivative Liability, Counterparty netting offset	112	144
Derivative Liability, Collateral, Right to Reclaim Cash, Offset	17	0
Net derivative positions	(48)	(61)
Other Long-Term Liabilities | Derivatives designated as hedges | Foreign exchange
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	(60)	(170)
Other Long-Term Liabilities | Derivatives designated as hedges | Interest rate
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	0	0
Other Long-Term Liabilities | Derivatives designated as hedges | Other Derivative
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	0	0
Other Long-Term Liabilities | Derivatives not designated as hedges | Foreign exchange
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	(44)	(19)
Other Long-Term Liabilities | Derivatives not designated as hedges | Interest rate
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	$ (73)	$ (16)