Segment, Geographic and Revenue Information (Additional Information - Investment Management) (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|
| Segment Reporting [Abstract] | |||
| Segment | ms:InvestmentManagementSegmentMember | ||
| Net cumulative unrealized performance-based fees at risk of reversing | $ 434 | $ 442 | |
| Fee waivers | $ 56 | $ 86 | $ 91 |