Derivatives, Hedging Activities and Interest Expense - Additional Information (Details) - USD ($) $ in Millions	Sep. 30, 2015	Mar. 31, 2015
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Aggregate fair value of derivative instruments in a net liability position	$ 55
Collateral held	121	$ 145
Collateral posted in excess of the fair value of derivative liabilities	11	2
Collateral posted	$ 1,596	1,694
Collateral held in excess of the fair value of derivative assets		$ 10

Amount of obligation to return cash collateral under master netting arrangements offset against derivative assets.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

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-Name Accounting Standards Codification

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Amount of obligation to return cash collateral under master netting arrangements that have not been offset against derivative assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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Amount of right to receive cash collateral under master netting arrangements that have not been offset against derivative liabilities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

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-URI http://asc.fasb.org/extlink&oid=51825145&loc=SL20226016-175313

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No definition available.

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Amount of right to receive cash collateral under master netting arrangements offset against derivative liabilities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

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-Paragraph 3

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-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

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The aggregate fair value amounts of derivative instruments that contain credit-risk-related contingent features that are in a net liability position at the end of the reporting period. For nonderivative instruments that are designated and qualify as hedging instruments, the fair value amounts are the carrying value of the nonderivative hedging instrument, including the adjustment for the foreign currency transaction gain (loss) on that instrument.

+ References

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