Condensed MUFG Americas Holdings Corporation Unconsolidated Financial Statements (Parent Company) - Statement of Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash Flows from Operating Activities:
Net Income	$ (751)	$ 1,049	$ 1,034
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Other, net	59	(18)	11
Cash Flows from Financing Activities:
Proceeds from (Repurchase of) Equity	0	(2,496)	0
Other, net	(96)	(115)	(71)
Net increase (decrease) in cash and cash equivalents	1,297	4,870	(2,306)
Cash, cash equivalents and restricted cash at beginning of period	8,350	3,392
Cash, cash equivalents and restricted cash at end of period	9,641	8,350	3,392
MUFG Americas Holdings Corporation
Cash Flows from Operating Activities:
Net Income	(734)	1,073	1,077
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Equity in undistributed net income of subsidiaries less dividends received	1,270	676	(750)
Other, net	(743)	(9)	2
Net cash provided by (used in) operating activities	(207)	1,740	329
Cash Flows from Investing Activities:
Investments in and advances to subsidiaries	(1,585)	(2,612)	(5,050)
Repayment of investments in and advances to subsidiaries	1,634	2,411	1,495
Net cash provided by (used in) investing activities	49	(201)	(3,555)
Cash Flows from Financing Activities:
Proceeds from advances from subsidiaries	0	0	200
Repayment of advances from subsidiaries	0	0	(200)
Proceeds from issuance of long-term debt	1,890	6,500	3,525
Repayment of long-term debt	(1,631)	(6,145)	0
Dividends paid	0	0	(500)
Proceeds from (Repurchase of) Equity	0	(2,496)	0
Other, net	0	0	0
Net cash provided by (used in) financing activities	259	(2,141)	3,025
Net increase (decrease) in cash and cash equivalents	101	(602)	(201)
Cash, cash equivalents and restricted cash at beginning of period	739	1,341	1,542
Cash, cash equivalents and restricted cash at end of period	$ 840	$ 739	$ 1,341