FAIR VALUE OF FINANCIAL INSTRUMENTS - Amortized Cost for which Fair Value is Disclosed (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Disclosure of fair value measurement of liabilities [line items]
Financial liabilities	$ 193,217	$ 184,231
Not measured at fair value in statement of financial position but for which fair value is disclosed | Corporate borrowings | Level 1
Disclosure of fair value measurement of liabilities [line items]
Financial liabilities	10,443	7,841
Not measured at fair value in statement of financial position but for which fair value is disclosed | Corporate borrowings | Level 2
Disclosure of fair value measurement of liabilities [line items]
Financial liabilities	97	92
Not measured at fair value in statement of financial position but for which fair value is disclosed | Corporate borrowings | Level 3
Disclosure of fair value measurement of liabilities [line items]
Financial liabilities	0	0
Not measured at fair value in statement of financial position but for which fair value is disclosed | Property-specific borrowings | Level 1
Disclosure of fair value measurement of liabilities [line items]
Financial liabilities	3,406	6,467
Not measured at fair value in statement of financial position but for which fair value is disclosed | Property-specific borrowings | Level 2
Disclosure of fair value measurement of liabilities [line items]
Financial liabilities	57,927	52,386
Not measured at fair value in statement of financial position but for which fair value is disclosed | Property-specific borrowings | Level 3
Disclosure of fair value measurement of liabilities [line items]
Financial liabilities	69,766	70,875
Not measured at fair value in statement of financial position but for which fair value is disclosed | Subsidiary borrowings | Level 1
Disclosure of fair value measurement of liabilities [line items]
Financial liabilities	7,825	6,111
Not measured at fair value in statement of financial position but for which fair value is disclosed | Subsidiary borrowings | Level 2
Disclosure of fair value measurement of liabilities [line items]
Financial liabilities	3	299
Not measured at fair value in statement of financial position but for which fair value is disclosed | Subsidiary borrowings | Level 3
Disclosure of fair value measurement of liabilities [line items]
Financial liabilities	3,257	2,222
Not measured at fair value in statement of financial position but for which fair value is disclosed | Subsidiary equity obligations | Level 1
Disclosure of fair value measurement of liabilities [line items]
Financial liabilities	0	0
Not measured at fair value in statement of financial position but for which fair value is disclosed | Subsidiary equity obligations | Level 2
Disclosure of fair value measurement of liabilities [line items]
Financial liabilities	73	73
Not measured at fair value in statement of financial position but for which fair value is disclosed | Subsidiary equity obligations | Level 3
Disclosure of fair value measurement of liabilities [line items]
Financial liabilities	$ 2,169	$ 2,170