Pension and Other Benefit Plans - Reconciliation of Assets Valued Using Significant Unobservable Inputs (Details) - Pension Plans, Defined Benefit - USD ($) $ in Millions	12 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Fair value of plan assets at beginning of year	$ 11,574	$ 2,998
Changes due to exchange rates	818	(1,170)
Fair value of plan assets at end of year	11,343	11,574
Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Fair value of plan assets at beginning of year	887	348
Actual return on plan assets held at the reporting date	(13)	34
Purchases, sales, and settlements	217	443
Transfers in and / or out of Level 3	5
Changes due to exchange rates	(64)	62
Fair value of plan assets at end of year	$ 1,032	$ 887

Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from actual return (loss) on assets still held.

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

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- Definition

Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Amount of foreign currency translation gain (loss) which (increases) decreases benefit obligation of defined benefit plan.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)(5)
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- Definition

Amount, measured using unobservable input, of increase (decrease) in plan asset of defined benefit plan from purchase, sale and settlement of trade associated with underlying investment.

+ References

+ Details

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- Definition

Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan, for assets transferred into (out of) Level 3 of fair value hierarchy. Includes, but is not limited to, transfer due to change in observability of significant inputs.

+ References

+ Details

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- Details

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- Details

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