NOTES RECEIVABLE - Notes Receivable Expected Future Principal Payments (Net of Reserves and Unamortized Discounts and Interest Rates) (Details) $ in Millions	Dec. 31, 2019 USD ($)
Receivables [Abstract]
2020	$ 9
2021	32
2022	28
2023	2
2024	8
Thereafter	47
Senior, mezzanine, and other loans	$ 126
Weighted average interest rate at year-end 2019	5.60%
Range of stated interest rates at year-end 2018, minimum	0.00%
Range of stated interest rates at year-end 2018, maximum	9.00%

Notes Receivable, Future Principal Payments Receivable, After Year Five

No definition available.

Name:	mar_NotesReceivableFuturePrincipalPaymentsReceivableAfterYearFive
Namespace Prefix:	mar_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Notes Receivable, Future Principal Payments Receivable, Current

+ References

No definition available.

+ Details

Name:	mar_NotesReceivableFuturePrincipalPaymentsReceivableCurrent
Namespace Prefix:	mar_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Notes Receivable, Future Principal Payments Receivable, in Five Years

+ References

No definition available.

+ Details

Name:	mar_NotesReceivableFuturePrincipalPaymentsReceivableInFiveYears
Namespace Prefix:	mar_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Notes Receivable, Future Principal Payments Receivable, in Four Years

+ References

No definition available.

+ Details

Name:	mar_NotesReceivableFuturePrincipalPaymentsReceivableInFourYears
Namespace Prefix:	mar_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Notes Receivable, Future Principal Payments Receivable, in Three Years

+ References

No definition available.

+ Details

Name:	mar_NotesReceivableFuturePrincipalPaymentsReceivableInThreeYears
Namespace Prefix:	mar_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Notes Receivable, Future Principal Payments Receivable, in Two Years

+ References

No definition available.

+ Details

Name:	mar_NotesReceivableFuturePrincipalPaymentsReceivableInTwoYears
Namespace Prefix:	mar_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Upper limit of range of stated interest rates for total notes receivable as of the balance sheet date indicated.

+ References

No definition available.

+ Details

Name:	mar_NotesReceivableInterestRateStatedPercentageRateRangeMaximum
Namespace Prefix:	mar_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Lower limit of range of stated interest rates for total notes receivable as of the balance sheet date indicated.

+ References

No definition available.

+ Details

Name:	mar_NotesReceivableInterestRateStatedPercentageRateRangeMinimum
Namespace Prefix:	mar_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Weighted average interest rate for total notes receivable as of the balance sheet date indicated.

+ References

No definition available.

+ Details

Name:	mar_NotesReceivableWeightedAverageInterestRate
Namespace Prefix:	mar_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount, after allowance for credit loss, of financing receivable. Excludes financing receivable covered under loss sharing agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919230-210447

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(3))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=118952595&loc=d3e4428-111522

+ Details

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

- References

No definition available.

+ Details

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