Financial Instruments - Summary of Cash and Available-for-Sale Securities by Significant Investment Category (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 14,509	$ 10,774
Fair Value, Inputs, Level 2
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	19,557	17,622
Unrealized Gains	0	0
Unrealized Losses	(271)	(52)
Estimated Fair Value	19,286	17,570
Cash and cash equivalents \| Fair Value, Inputs, Level 2
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	5,048	6,848
Current Marketable Securities \| Fair Value, Inputs, Level 2
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	5,067	3,879
Non- Current Marketable Securities \| Fair Value, Inputs, Level 2
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	9,171	6,843
Cash and cash equivalents \| Fair Value, Inputs, Level 1
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	5,048	6,848
Unrealized Gains	0	0
Unrealized Losses	0	0
Estimated Fair Value	5,048	6,848
Cash and cash equivalents \| Cash and cash equivalents \| Fair Value, Inputs, Level 1
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	5,048	6,848
Cash and cash equivalents \| Current Marketable Securities \| Fair Value, Inputs, Level 1
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	0	0
Cash and cash equivalents \| Non- Current Marketable Securities \| Fair Value, Inputs, Level 1
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	0	0
Certificates of deposit \| Fair Value, Inputs, Level 2
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	251	80
Unrealized Gains	0	0
Unrealized Losses	0	0
Estimated Fair Value	251	80
Certificates of deposit \| Cash and cash equivalents \| Fair Value, Inputs, Level 2
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	0	0
Certificates of deposit \| Current Marketable Securities \| Fair Value, Inputs, Level 2
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	251	80
Certificates of deposit \| Non- Current Marketable Securities \| Fair Value, Inputs, Level 2
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	0	0
U.S. treasury bills \| Fair Value, Inputs, Level 2
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	515	479
Unrealized Gains	0	0
Unrealized Losses	(2)	0
Estimated Fair Value	513	479
U.S. treasury bills \| Cash and cash equivalents \| Fair Value, Inputs, Level 2
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	0	0
U.S. treasury bills \| Current Marketable Securities \| Fair Value, Inputs, Level 2
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	513	479
U.S. treasury bills \| Non- Current Marketable Securities \| Fair Value, Inputs, Level 2
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	0	0
U.S. treasury notes \| Fair Value, Inputs, Level 2
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	7,956	6,595
Unrealized Gains	0	0
Unrealized Losses	(147)	(31)
Estimated Fair Value	7,809	6,564
U.S. treasury notes \| Cash and cash equivalents \| Fair Value, Inputs, Level 2
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	0	0
U.S. treasury notes \| Current Marketable Securities \| Fair Value, Inputs, Level 2
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	2,820	1,984
U.S. treasury notes \| Non- Current Marketable Securities \| Fair Value, Inputs, Level 2
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	4,989	4,580
Corporate debt securities \| Fair Value, Inputs, Level 2
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	5,665	3,508
Unrealized Gains	0	0
Unrealized Losses	(117)	(20)
Estimated Fair Value	5,548	3,488
Corporate debt securities \| Cash and cash equivalents \| Fair Value, Inputs, Level 2
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	0	0
Corporate debt securities \| Current Marketable Securities \| Fair Value, Inputs, Level 2
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	1,470	1,323
Corporate debt securities \| Non- Current Marketable Securities \| Fair Value, Inputs, Level 2
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	4,078	2,165
Government debt securities \| Fair Value, Inputs, Level 2
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	122	112
Unrealized Gains	0	0
Unrealized Losses	(5)	(1)
Estimated Fair Value	117	111
Government debt securities \| Cash and cash equivalents \| Fair Value, Inputs, Level 2
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	0	0
Government debt securities \| Current Marketable Securities \| Fair Value, Inputs, Level 2
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	13	13
Government debt securities \| Non- Current Marketable Securities \| Fair Value, Inputs, Level 2
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	$ 104	$ 98

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27161-111563

+ Details

Name:	us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27161-111563

+ Details

Name:	us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454

+ Details

Name:	us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(6))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=124260329&loc=d3e26610-111562

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27161-111563

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesDebtSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

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.

+ References

No definition available.

+ Details

Name:	us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_CashAndCashEquivalentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=mrna_CurrentMarketableSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=mrna_NoncurrentMarketableSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CashAndCashEquivalentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CertificatesOfDepositMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USTreasurySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USGovernmentDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: