Earnings per Common Share - Summary (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Earnings applicable to Morgan Stanley common shareholders	$ 2,031	$ 2,267	$ 4,367	$ 4,842
Net Income (Loss) Available to Common Stockholders, Basic [Abstract]
Weighted average common shares outstanding (shares)	1,634	1,720	1,646	1,730
Earnings per basic common share (USD per share)	$ 1.24	$ 1.32	$ 2.65	$ 2.80
Net Income (Loss) Available to Common Stockholders, Diluted [Abstract]
Weighted average common shares outstanding (shares)	1,634	1,720	1,646	1,730
Effect of dilutive RSUs and PSUs (shares)	21	28	20	30
Weighted average common shares outstanding and common stock equivalents (shares)	1,655	1,748	1,666	1,760
Earnings per diluted common share (USD per share)	$ 1.23	$ 1.30	$ 2.62	$ 2.75
Weighted average antidilutive RSUs (excluded from the computation of diluted EPS) (shares)	0	1	3	1