v3.10.0.1
Equity Method Investments (Investees) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Equity Method Investments      
Income from equity method investments $ 20 $ (34) $ (79)
MUMSS      
Equity Method Investments      
Voting interest 40.00%    
Income from equity method investments $ 105 $ 123 $ 93
MUMSS | MUFG      
Equity Method Investments      
Voting interest 60.00%