Derivative Instruments and Hedging Activities Derivative Instruments and Hedging Activities - Offsetting Assets and Liabilities (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Sep. 30, 2014	Mar. 31, 2014
Offsetting Derivative Assets and Liabilities [Abstract]
Gross amount recognized, derivative assets	$ 307	$ 243	$ 255
Gross amount recognized, derivative liabilities	1,733	1,813	951
Gross amount eligible for offsetting, derivative assets	(25)	(11)	(12)
Gross amount eligible for offsetting, derivative liabilities	(25)	(11)	(12)
Net derivative amount, derivative assets	282us-gaap_DerivativeAssets	232us-gaap_DerivativeAssets	243us-gaap_DerivativeAssets
Net derivative amount, derivative liabilities	$ 1,708us-gaap_DerivativeLiabilities	$ 1,802us-gaap_DerivativeLiabilities	$ 939us-gaap_DerivativeLiabilities

Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value, after offset of derivative liability, of financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, before offset against an obligation to return collateral under a master netting arrangement. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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- Definition

Fair value, after offset of derivative asset, of financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, elected not to be and before offset against a right to receive collateral under a master netting arrangement. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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- Definition

Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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