Commercial Paper and Other Short-Term Borrowings - Summary of Commercial Paper and Other Short-Term Borrowings (Details) $ in Millions, ¥ in Billions	Dec. 31, 2018 USD ($)	Dec. 31, 2018 JPY (¥)	Dec. 31, 2017 USD ($)
Commercial Paper and Short-Term Borrowings
Total commercial paper and other short-term borrowings	$ 9,263		$ 7,066
MUB
Commercial Paper and Short-Term Borrowings
Total commercial paper and other short-term borrowings	8,182		6,097
MUAH
Commercial Paper and Short-Term Borrowings
Short-term debt due to MUFG Bank, Ltd., with weighted average interest rates of 3.01% and 1.88% at December 31, 2018 and December 31, 2017, respectively	145		168
Total commercial paper and other short-term borrowings	1,081		$ 969
Weighted average interest rate			1.88%
Commercial paper \| MUB
Commercial Paper and Short-Term Borrowings
Commercial paper, with a weighted average interest rate of 2.39% and 1.26% at December 31, 2018 and December 31, 2017, respectively	$ 382		$ 347
Weighted average interest rate	2.39%	2.39%	1.26%
Federal Home Loan Bank advances \| MUB
Commercial Paper and Short-Term Borrowings
Federal Home Loan Bank advances, with a weighted average interest rate of 2.52% and 1.42% at December 31, 2018 and December 31, 2017, respectively	$ 7,800		$ 5,750
Weighted average interest rate	2.52%	2.52%	1.42%
Parent Company [Member] \| MUAH
Commercial Paper and Short-Term Borrowings
Weighted average interest rate	3.01%	3.01%
Affiliated Entity \| MUAH
Commercial Paper and Short-Term Borrowings
Short-term debt due to affiliates, with weighted average interest rates of (-0.07)% and (-0.09)% at December 31, 2018 and December 31, 2017, respectively	$ 936	¥ 103	$ 801
Weighted average interest rate	(0.07%)	(0.07%)	(0.09%)

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Carrying value as of the balance sheet date of short-term borrowings using unsecured obligations issued by banks, corporations and other borrowers to investors. The maturities of these money market securities generally do not exceed 270 days.

+ References

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Amount of borrowings from a bank classified as other, maturing within one year or operating cycle, if longer.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

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Weighted average interest rate of short-term debt outstanding calculated at point in time.

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