Commercial Paper and Other Short-Term Borrowings (Details) ¥ in Billions	6 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2017 JPY (¥)	Dec. 31, 2016 USD ($)
Short-term Debt [Line Items]
Total commercial paper and other short-term borrowings	$ 6,195,000,000		$ 2,360,000,000
MUFG Union Bank N.A
Short-term Debt [Line Items]
Total commercial paper and other short-term borrowings	$ 5,028,000,000		$ 989,000,000
MUFG Union Bank N.A | Federal Funds Purchased
Short-term Debt [Line Items]
Weighted average interest rate at period end	1.00%	1.00%	0.50%
Federal funds purchased	$ 1,000,000		$ 26,000,000
MUFG Union Bank N.A | Commercial Paper
Short-term Debt [Line Items]
Weighted average interest rate at period end	0.81%	0.81%	0.55%
Commercial paper	$ 427,000,000		$ 263,000,000
MUFG Union Bank N.A | Federal Home Loan Bank Advances
Short-term Debt [Line Items]
Weighted average interest rate at period end	0.94%	0.94%	0.59%
Federal home loan bank advances	$ 4,600,000,000		$ 700,000,000
MUFG Americas Holding Corporation
Short-term Debt [Line Items]
Weighted average interest rate at period end	1.57%	1.57%	0.49%
Short-term Debt Due to Parent	$ 357,000,000		$ 679,000,000
Total commercial paper and other short-term borrowings	1,167,000,000		$ 1,371,000,000
MUFG Americas Holding Corporation | Line of Credit
Short-term Debt [Line Items]
Maximum borrowing capacity	$ 1,400,000,000.0
Line of Credit Facility, Extension Period	100 days
MUFG Americas Holding Corporation | Affiliated Entity
Short-term Debt [Line Items]
Weighted average interest rate at period end	(0.07%)	(0.07%)	(0.04%)
Short term debt due to affiliates	$ 810,000,000	¥ 91	$ 692,000,000