Derivative Instruments - Notional Balances and Gross Fair Values of Derivatives (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Mar. 31, 2015
Derivatives Fair Value [Line Items]
Gross derivative assets	$ 212	$ 237
Counterparty netting, Assets	(74)	(97)
Net derivative assets	138	140
Gross derivative liabilities	244	371
Counterparty netting, Liabilities	(74)	(97)
Net derivative liabilities	170	274
Interest rate swaps
Derivatives Fair Value [Line Items]
Notional balances	48,571	49,216
Gross derivative assets	210	236
Gross derivative liabilities	56	115
Cross currency swaps
Derivatives Fair Value [Line Items]
Notional balances	2,739	1,385
Gross derivative assets	2	1
Gross derivative liabilities	$ 188	$ 256

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 45
-Paragraph 5
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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.

+ References

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Fair value, before 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 elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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