Income Taxes - Gross Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits at beginning of period	$ 958	$ 1,052	$ 1,183
Additions based on tax positions related to prior years	53	20	78
Reductions based on tax positions related to prior years	(5)	(168)	(234)
Additions based on tax positions related to current year	755	82	68
Reductions based on settlements	(8)	(8)	(13)
Reductions based on the lapse of the applicable statutes of limitations	(12)	(13)	(25)
Exchange rate fluctuations	13	(7)	(5)
Unrecognized tax benefits at end of period	$ 1,754	$ 958	$ 1,052

Unrecognized Tax Benefits, Increase (Decrease) Resulting from Foreign Currency Translation

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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.

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- Definition

Amount of unrecognized tax benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 45
-Paragraph 10B
-URI http://asc.fasb.org/extlink&oid=120406818&loc=SL37586934-109318

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15A
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=SL6600010-109319

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- Definition

Amount of decrease in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15A
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-URI http://asc.fasb.org/extlink&oid=84230637&loc=SL6600010-109319

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- Definition

Amount of decrease in unrecognized tax benefits resulting from settlements with taxing authorities.

+ References

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

Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Amount of increase in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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- Definition

Amount of decrease in unrecognized tax benefits resulting from lapses of applicable statutes of limitations.

+ References

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