Condensed MUFG Americas Holdings Corporation Unconsolidated Financial Statements (Parent Company) - Statements of Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income:
Total income	$ 5,484	$ 5,214	$ 5,278
Expense:
Other expense	4,277	3,984	3,782
Income before income taxes and including noncontrolling interests	1,101	1,333	1,341
Income tax benefit	(52)	(299)	(419)
Equity in undistributed net income of subsidiaries less dividends received:
Net Income Including Noncontrolling Interests	1,049	1,034	922
MUFG Americas Holdings Corporation
Income:
Interest income on advances to subsidiaries and deposits in bank	137	79	22
Rental Income	15	15	16
Total income	1,947	465	38
Expense:
Interest expense	194	144	75
Other expense	17	14	19
Total expense	211	158	94
Income before income taxes and including noncontrolling interests	1,736	307	(56)
Income tax benefit	13	20	22
Income (loss) before equity in undistributed net income of subsidiaries	1,749	327	(34)
Equity in undistributed net income of subsidiaries less dividends received:
Bank subsidiary	(697)	366	900
Nonbank subsidiaries	21	384	124
Net Income Including Noncontrolling Interests	1,073	1,077	990
Bank Subsidiary | MUFG Americas Holdings Corporation
Income:
Investment Income, Dividend	1,700	320	0
Nonbank Subsidiary | MUFG Americas Holdings Corporation
Income:
Investment Income, Dividend	$ 95	$ 51	$ 0