Segment, Geographic and Revenue Information - Selected Financial Information by Business Segment (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information
Investment banking	$ 1,635	$ 1,567	$ 4,467	$ 4,994
Trading	2,608	2,752	8,781	9,815
Investments	87	136	801	409
Commissions and fees	990	932	2,935	3,144
Asset management	3,363	3,251	9,632	9,632
Other	131	298	685	748
Total non-interest revenues	8,814	8,936	27,301	28,742
Interest income	4,350	3,627	13,146	9,781
Interest expense	3,132	2,691	9,885	6,964
Net interest	1,218	936	3,261	2,817
Net revenues	10,032	9,872	30,562	31,559
Income from continuing operations before income taxes	2,710	2,851	8,568	9,380
Provision for income taxes	492	696	1,636	2,050
Income from continuing operations	2,218	2,155	6,932	7,330
Income (loss) from discontinued operations, net of income taxes	0	(1)	0	(5)
Net income	2,218	2,154	6,932	7,325
Net income (loss) applicable to noncontrolling interests	45	42	129	108
Net income applicable to Morgan Stanley	2,173	2,112	6,803	7,217
Segment Reporting Information, Additional Information [Abstract]
Revenues to be recorded in the remainder of 2019	57		57
Revenues to be recorded in 2020	132		132
Revenues to be recorded thereafter	239		239
Revenue recognized in the current period, where some or all services were performed in prior periods	841	$ 804	1,995	$ 2,192
Minimum
Segment Reporting Information, Additional Information [Abstract]
Revenues to be recorded in 2021 through 2025	63		63
Maximum
Segment Reporting Information, Additional Information [Abstract]
Revenues to be recorded in 2021 through 2025	$ 89		$ 89
Accounting Standards Update 2014-09
Segment Reporting Information, Additional Information [Abstract]
Proportion of Investment banking revenue determined under the Revenue from Contracts with Customers accounting update	85.00%	85.00%	90.00%	85.00%
I/E
Segment Reporting Information
Investment banking	$ (18)	$ (21)	$ (55)	$ (60)
Trading	12	17	37	44
Investments	0	0	0	0
Commissions and fees	(70)	(66)	(205)	(212)
Asset management	(40)	(38)	(115)	(114)
Other	(1)	(1)	(6)	(5)
Total non-interest revenues	(117)	(109)	(344)	(347)
Interest income	(144)	(229)	(464)	(692)
Interest expense	(148)	(229)	(476)	(695)
Net interest	4	0	12	3
Net revenues	(113)	(109)	(332)	(344)
Income from continuing operations before income taxes	0	(1)	(4)	(1)
Provision for income taxes	0	0	(1)	0
Income from continuing operations	0	(1)	(3)	(1)
Income (loss) from discontinued operations, net of income taxes		0		0
Net income	0	(1)	(3)	(1)
Net income (loss) applicable to noncontrolling interests	0	0	0	0
Net income applicable to Morgan Stanley	0	(1)	(3)	(1)
IS | Operating Segments
Segment Reporting Information
Investment banking	1,535	1,459	4,158	4,671
Trading	2,533	2,573	8,221	9,344
Investments	(18)	96	257	234
Commissions and fees	643	589	1,889	2,007
Asset management	100	112	310	324
Other	51	244	416	548
Total non-interest revenues	4,844	5,073	15,251	17,128
Interest income	3,112	2,425	9,457	6,424
Interest expense	2,933	2,569	9,376	6,809
Net interest	179	(144)	81	(385)
Net revenues	5,023	4,929	15,332	16,743
Income from continuing operations before income taxes	1,307	1,556	4,365	5,480
Provision for income taxes	189	397	703	1,169
Income from continuing operations	1,118	1,159	3,662	4,311
Income (loss) from discontinued operations, net of income taxes		(3)		(7)
Net income	1,118	1,156	3,662	4,304
Net income (loss) applicable to noncontrolling interests	45	36	97	100
Net income applicable to Morgan Stanley	1,073	1,120	3,565	4,204
IS | Operating Segments | Advisory
Segment Reporting Information
Investment banking	550	510	1,462	1,702
IS | Operating Segments | Underwriting
Segment Reporting Information
Investment banking	985	949	2,696	2,969
WM | Operating Segments
Segment Reporting Information
Investment banking	118	129	365	383
Trading	61	160	525	404
Investments	0	0	1	3
Commissions and fees	416	409	1,250	1,349
Asset management	2,639	2,573	7,544	7,582
Other	81	58	281	195
Total non-interest revenues	3,315	3,329	9,966	9,916
Interest income	1,378	1,412	4,139	4,012
Interest expense	335	342	950	830
Net interest	1,043	1,070	3,189	3,182
Net revenues	4,358	4,399	13,155	13,098
Income from continuing operations before income taxes	1,238	1,194	3,669	3,511
Provision for income taxes	276	281	830	808
Income from continuing operations	962	913	2,839	2,703
Income (loss) from discontinued operations, net of income taxes		0		0
Net income	962	913	2,839	2,703
Net income (loss) applicable to noncontrolling interests	0	0	0	0
Net income applicable to Morgan Stanley	962	913	2,839	2,703
IM | Operating Segments
Segment Reporting Information
Investment banking	0	0	(1)	0
Trading	2	2	(2)	23
Investments	105	40	543	172
Commissions and fees	1	0	1	0
Asset management	664	604	1,893	1,840
Other	0	(3)	(6)	10
Total non-interest revenues	772	643	2,428	2,045
Interest income	4	19	14	37
Interest expense	12	9	35	20
Net interest	(8)	10	(21)	17
Net revenues	764	653	2,407	2,062
Income from continuing operations before income taxes	165	102	538	390
Provision for income taxes	27	18	104	73
Income from continuing operations	138	84	434	317
Income (loss) from discontinued operations, net of income taxes		2		2
Net income	138	86	434	319
Net income (loss) applicable to noncontrolling interests	0	6	32	8
Net income applicable to Morgan Stanley	$ 138	$ 80	$ 402	$ 311