Commercial Paper and Other Short-Term Borrowings (Details) ¥ in Billions	3 Months Ended
	Mar. 31, 2017 USD ($)	Mar. 31, 2017 JPY (¥)	Dec. 31, 2016 USD ($)
Short-term Debt [Line Items]
Total commercial paper and other short-term borrowings	$ 3,487,000,000		$ 2,360,000,000
MUFG Union Bank N.A
Short-term Debt [Line Items]
Total commercial paper and other short-term borrowings	$ 2,291,000,000		$ 989,000,000
MUFG Union Bank N.A | Federal Funds Purchased
Short-term Debt [Line Items]
Weighted average interest rate at period end	0.72%	0.72%	0.50%
Federal funds purchased	$ 40,000,000		$ 26,000,000
MUFG Union Bank N.A | Commercial Paper
Short-term Debt [Line Items]
Weighted average interest rate at period end	0.71%	0.71%	0.55%
Commercial paper, with a weighted average interest rate of 0.71% and 0.55% at March 31, 2017 and December 31, 2016, respectively	$ 651,000,000		$ 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	0.62%	0.62%	0.59%
Short-term Bank Loans and Notes Payable	$ 1,600,000,000		$ 700,000,000
MUFG Americas Holding Corporation
Short-term Debt [Line Items]
Weighted average interest rate at period end	1.47%	1.47%	0.49%
Short-term Debt Due to Parent	$ 425,000,000		$ 679,000,000
Total commercial paper and other short-term borrowings	1,196,000,000		$ 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	$ 771,000,000	¥ 86	$ 692,000,000