Other Assets - Equity Method Investments and Leases - Narrative (Details)	Dec. 31, 2021
Morgan Stanley MUFG Securities Co., Ltd.
Equity Method Investments
Voting/ economic interest (as a percent)	40.00%
Morgan Stanley MUFG Securities Co., Ltd. | IS
Equity Method Investments
Voting/ economic interest (as a percent)	51.00%
Morgan Stanley MUFG Securities Co., Ltd. | MUFG
Equity Method Investments
Voting/ economic interest (as a percent)	60.00%
Mitsubishi UFJ Morgan Stanley Securities Co., Ltd
Equity Method Investments
Voting/ economic interest (as a percent)	40.00%