Earnings per Common Share - Summary (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Earnings applicable to Morgan Stanley common shareholders	$ 2,060	$ 2,019	$ 6,427	$ 6,861
Net Income (Loss) Available to Common Stockholders, Basic [Abstract]
Weighted average common shares outstanding (shares)	1,604	1,697	1,632	1,719
Earnings per basic common share (USD per share)	$ 1.28	$ 1.19	$ 3.94	$ 3.99
Net Income (Loss) Available to Common Stockholders, Diluted [Abstract]
Weighted average common shares outstanding (shares)	1,604	1,697	1,632	1,719
Effect of dilutive RSUs and PSUs (shares)	23	30	21	30
Weighted average common shares outstanding and common stock equivalents (shares)	1,627	1,727	1,653	1,749
Earnings per diluted common share (USD per share)	$ 1.27	$ 1.17	$ 3.89	$ 3.92
Weighted average antidilutive RSUs (excluded from the computation of diluted EPS) (shares)	0	1	2	1