RELATED PARTY TRANSACTIONS - Financial Data Resulting from Transactions with Related Parties, Income Statement Data (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Related Party Transaction [Line Items]
Total revenue	$ 5,289	$ 5,051	$ 5,409	$ 5,009	$ 5,251	$ 5,078	$ 5,211	$ 4,912	$ 20,758		$ 20,452		$ 15,407
Depreciation, amortization, and other		(52)	(58)	(54)					(226)	[1]	(229)	[1]	(119)	[1]
General, administrative, and other		(221)	(217)	(247)					(927)	[1]	(921)	[1]	(743)	[1]
Gains and other income, net		18	114	59					194	[1]	688	[1]	5	[1]
Interest income		5	6	5					22	[1]	38	[1]	35	[1]
Equity in earnings		61	21	13					103	[1]	40	[1]	9	[1]
Equity Method Investment
Related Party Transaction [Line Items]
Depreciation, amortization, and other									(2)		(3)		(1)
General, administrative, and other									0		(1)		0
Gains and other income, net									51		658		1
Interest income									0		4		5
Equity in earnings									103		40		9
Base management fees
Related Party Transaction [Line Items]
Gross fee revenues		279	300	273					1,140	[1]	1,102	[1]	806	[1]
Base management fees | Equity Method Investment
Related Party Transaction [Line Items]
Gross fee revenues									25		28		18
Incentive management fees
Related Party Transaction [Line Items]
Gross fee revenues		151	176	155					649	[1]	607	[1]	425	[1]
Incentive management fees | Equity Method Investment
Related Party Transaction [Line Items]
Gross fee revenues									12		15		10
Net fee revenues
Related Party Transaction [Line Items]
Gross fee revenues		932	951	845					3,638		3,295		2,388
Contract investment amortization		(13)	(13)	(18)					(58)	[1]	(50)	[1]	(40)	[1]
Total revenue		919	938	827					3,580		3,245		2,348
Net fee revenues | Equity Method Investment
Related Party Transaction [Line Items]
Contract investment amortization									(2)		(2)		(2)
Owned, leased, and other
Related Party Transaction [Line Items]
Total revenue		397	423	406					1,635	[1]	1,752	[1]	1,125	[1]
Reimbursed expenses		(315)	(334)	(336)					(1,306)		(1,411)		(901)
Owned, leased, and other | Equity Method Investment
Related Party Transaction [Line Items]
Total revenue									0		2		0
Reimbursements
Related Party Transaction [Line Items]
Total revenue		3,735	4,048	3,776					15,543	[1]	15,455	[1]	11,934	[1]
Reimbursed expenses		$ (3,855)	$ (3,964)	$ (3,808)					(15,778)	[1]	(15,228)	[1]	(11,834)	[1]
Reimbursements | Equity Method Investment
Related Party Transaction [Line Items]
Total revenue									332		356		222
Reimbursed expenses									$ (337)		$ (356)		$ (222)

[1] See Footnote 18. Related Party Transactions for disclosure of related party amounts.