Long-Term Debt (Details) - USD ($)		3 Months Ended	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Debt Instrument
Long-term debt	$ 11,333,000,000	$ 11,333,000,000	$ 11,410,000,000
Parent Company
Debt Instrument
Long-term debt	6,991,000,000	6,991,000,000	3,470,000,000
Parent Company | Senior Debt Obligations [Member] | Floating rate senior notes due February 2018. These notes, which bear interest at 0.57% above 3-month LIBOR, had a rate of 1.61% at March 31, 2017 and 1.46% at December 31, 2016
Debt Instrument
Long-term debt	$ 250,000,000	$ 250,000,000	$ 250,000,000
Long-term Debt, Weighted Average Interest Rate	1.61%	1.61%	1.46%
Parent Company | Senior Debt Obligations [Member] | Floating rate senior notes due February 2018. These notes, which bear interest at 0.57% above 3-month LIBOR, had a rate of 1.61% at March 31, 2017 and 1.46% at December 31, 2016 | London Interbank Offered Rate LIBOR
Debt Instrument
Interest rate above variable interest rate (as a percent)		0.57%	0.57%
Parent Company | Senior Debt Obligations [Member] | Fixed rate 1.625% notes due February 2018
Debt Instrument
Long-term debt	$ 449,000,000	$ 449,000,000	$ 449,000,000
Debt instrument, Fixed interest rate (as a percent)	1.625%	1.625%	1.625%
Parent Company | Senior Debt Obligations [Member] | Fixed rate 2.25% notes due February 2020
Debt Instrument
Long-term debt	$ 997,000,000	$ 997,000,000	$ 997,000,000
Debt instrument, Fixed interest rate (as a percent)	2.25%	2.25%	2.25%
Parent Company | Senior Debt Obligations [Member] | Fixed rate 3.50% notes due June 2022
Debt Instrument
Long-term debt	$ 397,000,000	$ 397,000,000	$ 397,000,000
Debt instrument, Fixed interest rate (as a percent)	3.50%	3.50%	3.50%
Parent Company | Senior Debt Obligations [Member] | Fixed rate 3.00% notes due February 2025
Debt Instrument
Long-term debt	$ 496,000,000	$ 496,000,000	$ 496,000,000
Debt instrument, Fixed interest rate (as a percent)	3.00%	3.00%	3.00%
Parent Company | Senior Debt Obligations [Member] | Floating rate debt due September 2020. This note, which bears interest at 0.85% above 3-month LIBOR, had a rate of 2.00% at March 31, 2017
Debt Instrument
Long-term debt	$ 3,500,000,000	$ 3,500,000,000	$ 0
Proceeds from Issuance of Long-term Debt		$ 3,500,000,000
Long-term Debt, Weighted Average Interest Rate	2.00%	2.00%
Prepayment of long term debt		$ 500,000
Parent Company | Senior Debt Obligations [Member] | Floating rate debt due September 2020. This note, which bears interest at 0.85% above 3-month LIBOR, had a rate of 2.00% at March 31, 2017 | London Interbank Offered Rate LIBOR
Debt Instrument
Interest rate above variable interest rate (as a percent)		0.85%
Parent Company | Senior Debt Obligations [Member] | Floating rate debt due December 2023. This note, which bears interest at 0.76% above 3-month EURIBOR, had a rate of 0.76% at March 31, 2017
Debt Instrument
Long-term debt	$ 21,000,000	$ 21,000,000	0
Long-term Debt, Weighted Average Interest Rate	0.76%	0.76%
Parent Company | Senior Debt Obligations [Member] | Floating rate debt due December 2023. This note, which bears interest at 0.76% above 3-month EURIBOR, had a rate of 0.76% at March 31, 2017 | London Interbank Offered Rate LIBOR
Debt Instrument
Interest rate above variable interest rate (as a percent)		0.76%
Parent Company | Senior Debt Obligations [Member] | Floating rate debt due March 2020. This note, which bears interest at 0.86% above 3-month LIBOR, had a rate of 1.99% at March 31, 2017 and 1.82% at December 31, 2016
Debt Instrument
Long-term debt	$ 545,000,000	$ 545,000,000	$ 545,000,000
Long-term Debt, Weighted Average Interest Rate	1.99%	1.99%	1.82%
Parent Company | Senior Debt Obligations [Member] | Floating rate debt due March 2020. This note, which bears interest at 0.86% above 3-month LIBOR, had a rate of 1.99% at March 31, 2017 and 1.82% at December 31, 2016 | London Interbank Offered Rate LIBOR
Debt Instrument
Interest rate above variable interest rate (as a percent)		0.86%	0.86%
Parent Company | Subordinated Debt | Floating rate subordinated debt due December 2023. This note, which bears interest at 1.38% above 3-month LIBOR, had a rate of 2.53% at March 31, 2017 and 2.38% at December 31, 2016
Debt Instrument
Long-term debt	$ 300,000,000	$ 300,000,000	$ 300,000,000
Long-term Debt, Weighted Average Interest Rate	2.53%	2.53%	2.38%
Parent Company | Subordinated Debt | Floating rate subordinated debt due December 2023. This note, which bears interest at 1.38% above 3-month LIBOR, had a rate of 2.53% at March 31, 2017 and 2.38% at December 31, 2016 | London Interbank Offered Rate LIBOR
Debt Instrument
Interest rate above variable interest rate (as a percent)		1.38%	1.38%
Parent Company | Junior subordinated debt payable to trusts | Floating rate note due September 2036. This note had an interest rate of 2.83% at March 31, 2017 and 2.66% at December 31, 2016
Debt Instrument
Long-term debt	$ 36,000,000	$ 36,000,000	$ 36,000,000
Long-term Debt, Weighted Average Interest Rate	2.83%	2.83%	2.66%
MUFG Union Bank N.A
Debt Instrument
Long-term debt	$ 3,060,000,000	$ 3,060,000,000	$ 6,557,000,000
MUFG Union Bank N.A | Senior Debt Obligations [Member] | Floating rate notes due May 2017. These notes, which bear interest at 0.40% above 3-month LIBOR, had a rate of 1.43% at March 31, 2017 and 1.28% at December 31, 2016
Debt Instrument
Long-term debt	$ 250,000,000	$ 250,000,000	$ 250,000,000
Long-term Debt, Weighted Average Interest Rate	1.43%	1.43%	1.28%
MUFG Union Bank N.A | Senior Debt Obligations [Member] | Floating rate notes due May 2017. These notes, which bear interest at 0.40% above 3-month LIBOR, had a rate of 1.43% at March 31, 2017 and 1.28% at December 31, 2016 | London Interbank Offered Rate LIBOR
Debt Instrument
Interest rate above variable interest rate (as a percent)		0.40%	0.40%
MUFG Union Bank N.A | Senior Debt Obligations [Member] | Fixed rate 2.125% notes due June 2017
Debt Instrument
Long-term debt	$ 500,000,000	$ 500,000,000	$ 500,000,000
Debt instrument, Fixed interest rate (as a percent)	2.125%	2.125%	2.125%
MUFG Union Bank N.A | Senior Debt Obligations [Member] | Fixed rate 2.625% notes due September 2018
Debt Instrument
Long-term debt	$ 999,000,000	$ 999,000,000	$ 999,000,000
Debt instrument, Fixed interest rate (as a percent)	2.625%	2.625%	2.625%
MUFG Union Bank N.A | Senior Debt Obligations [Member] | Fixed rate 2.250% notes due May 2019
Debt Instrument
Long-term debt	$ 500,000,000	$ 500,000,000	$ 500,000,000
Debt instrument, Fixed interest rate (as a percent)	2.25%	2.25%	2.25%
MUFG Union Bank N.A | Senior Debt Obligations [Member] | Floating rate debt due January 2018. This note, which bears interest at 0.85% above 1-month LIBOR, had a rate of 1.47% at December 31, 2016
Debt Instrument
Long-term debt	$ 0	$ 0	$ 1,000,000,000
Long-term Debt, Weighted Average Interest Rate			1.47%
MUFG Union Bank N.A | Senior Debt Obligations [Member] | Floating rate debt due January 2018. This note, which bears interest at 0.85% above 1-month LIBOR, had a rate of 1.47% at December 31, 2016 | London Interbank Offered Rate LIBOR
Debt Instrument
Interest rate above variable interest rate (as a percent)		0.85%	0.85%
MUFG Union Bank N.A | Senior Debt Obligations [Member] | Floating rate debt due January 2018. This note, which bears interest at 0.87% above 1-month LIBOR, had a rate of 1.49% at December 31, 2016
Debt Instrument
Long-term debt	0	$ 0	$ 1,500,000,000
Long-term Debt, Weighted Average Interest Rate			1.49%
MUFG Union Bank N.A | Senior Debt Obligations [Member] | Floating rate debt due January 2018. This note, which bears interest at 0.87% above 1-month LIBOR, had a rate of 1.49% at December 31, 2016 | London Interbank Offered Rate LIBOR
Debt Instrument
Interest rate above variable interest rate (as a percent)		0.87%	0.87%
MUFG Union Bank N.A | Senior Debt Obligations [Member] | Floating rate debt due January 2018. This note, which bears interest at 1.03% above 1-month LIBOR, had a rate of 1.65% at December 31, 2016
Debt Instrument
Long-term debt	0	$ 0	$ 1,000,000,000
Long-term Debt, Weighted Average Interest Rate			1.65%
MUFG Union Bank N.A | Senior Debt Obligations [Member] | Floating rate debt due January 2018. This note, which bears interest at 1.03% above 1-month LIBOR, had a rate of 1.65% at December 31, 2016 | London Interbank Offered Rate LIBOR
Debt Instrument
Interest rate above variable interest rate (as a percent)		1.03%	1.03%
MUFG Union Bank N.A | Subordinated Debt | Floating rate subordinated debt due June 2023. This note, which bears interest at 1.20% above 3-month LIBOR, had a rate of 2.35% at March 31, 2017 and 2.20% at December 31, 2016
Debt Instrument
Long-term debt	$ 750,000,000	$ 750,000,000	$ 750,000,000
Long-term Debt, Weighted Average Interest Rate	2.35%	2.35%	2.20%
MUFG Union Bank N.A | Subordinated Debt | Floating rate subordinated debt due June 2023. This note, which bears interest at 1.20% above 3-month LIBOR, had a rate of 2.35% at March 31, 2017 and 2.20% at December 31, 2016 | London Interbank Offered Rate LIBOR
Debt Instrument
Interest rate above variable interest rate (as a percent)		1.20%	1.20%
MUFG Union Bank N.A | Other debt securities, Other
Debt Instrument
Long-term debt	$ 61,000,000	$ 61,000,000	$ 58,000,000
Other Subsidiaries, Excluding MUFG Bank, NA
Debt Instrument
Long-term debt	1,282,000,000	1,282,000,000	1,383,000,000
Other Subsidiaries, Excluding MUFG Bank, NA | Senior Debt Obligations [Member] | Various floating rate borrowings due between November 2020 and April 2021. These notes, which bear interest above 3-month LIBOR had a weighted-average interest rate of 1.15% at March 31, 2017 and 0.99% at December 31, 2016
Debt Instrument
Long-term debt	$ 250,000,000	$ 250,000,000	$ 250,000,000
Long-term Debt, Weighted Average Interest Rate	1.15%	1.15%	0.99%
Other Subsidiaries, Excluding MUFG Bank, NA | Senior Debt Obligations [Member] | Various fixed rate borrowings due between September 2019 and May 2023 with a weighted-average interest rate of 2.10% (between 1.71% and 2.44%) at March 31, 2017 and 2.15% (between 1.71% and 2.44%) at December 31, 2016
Debt Instrument
Long-term debt	$ 288,000,000	$ 288,000,000	$ 384,000,000
Long-term Debt, Weighted Average Interest Rate	2.10%	2.10%	2.15%
Other Subsidiaries, Excluding MUFG Bank, NA | Senior Debt Obligations [Member] | Various fixed rate borrowings due between September 2019 and May 2023 with a weighted-average interest rate of 2.10% (between 1.71% and 2.44%) at March 31, 2017 and 2.15% (between 1.71% and 2.44%) at December 31, 2016 | Minimum
Debt Instrument
Long-term Debt, Weighted Average Interest Rate	1.71%	1.71%	1.71%
Other Subsidiaries, Excluding MUFG Bank, NA | Senior Debt Obligations [Member] | Various fixed rate borrowings due between September 2019 and May 2023 with a weighted-average interest rate of 2.10% (between 1.71% and 2.44%) at March 31, 2017 and 2.15% (between 1.71% and 2.44%) at December 31, 2016 | Maximum
Debt Instrument
Long-term Debt, Weighted Average Interest Rate	2.44%	2.44%	2.44%
Other Subsidiaries, Excluding MUFG Bank, NA | Senior Debt Obligations [Member] | Various floating rate borrowings due between March 2018 and March 2019. These notes, which bear interest above 6-month LIBOR had a weighted-average interest rate of 2.68% (between 2.61% and 2.77%) at March 31, 2017 and 2.68% (between 2.61% and 2.77%) at December 31, 2016
Debt Instrument
Long-term Debt, Weighted Average Interest Rate	2.68%	2.68%	2.68%
Other Subsidiaries, Excluding MUFG Bank, NA | Senior Debt Obligations [Member] | Various floating rate borrowings due between March 2018 and March 2019. These notes, which bear interest above 6-month LIBOR had a weighted-average interest rate of 2.68% (between 2.61% and 2.77%) at March 31, 2017 and 2.68% (between 2.61% and 2.77%) at December 31, 2016 | Minimum
Debt Instrument
Long-term Debt, Weighted Average Interest Rate	2.61%	2.61%	2.61%
Other Subsidiaries, Excluding MUFG Bank, NA | Senior Debt Obligations [Member] | Various floating rate borrowings due between March 2018 and March 2019. These notes, which bear interest above 6-month LIBOR had a weighted-average interest rate of 2.68% (between 2.61% and 2.77%) at March 31, 2017 and 2.68% (between 2.61% and 2.77%) at December 31, 2016 | Maximum
Debt Instrument
Long-term Debt, Weighted Average Interest Rate	2.77%	2.77%	2.77%
Other Subsidiaries, Excluding MUFG Bank, NA | Subordinated Debt | Various floating rate borrowings due between March 2018 and March 2019. These notes, which bear interest above 6-month LIBOR had a weighted-average interest rate of 2.68% (between 2.61% and 2.77%) at March 31, 2017 and 2.68% (between 2.61% and 2.77%) at December 31, 2016
Debt Instrument
Long-term debt	$ 185,000,000	$ 185,000,000	$ 185,000,000
Other Subsidiaries, Excluding MUFG Bank, NA | Secured Debt | Various floating rate nonrecourse borrowings due to BTMU between June 2017 and December 2021. These notes, which bear interest above 1- or 3-month LIBOR had a weighted-average interest rate of 2.04% (between 1.23% and 2.91%) at March 31, 2017 and 1.67% (between 0.25% and 2.41%) at December 31, 2016
Debt Instrument
Long-term debt	$ 127,000,000	$ 127,000,000	$ 127,000,000
Long-term Debt, Weighted Average Interest Rate	2.04%	2.04%	1.67%
Other Subsidiaries, Excluding MUFG Bank, NA | Secured Debt | Various floating rate nonrecourse borrowings due to BTMU between June 2017 and December 2021. These notes, which bear interest above 1- or 3-month LIBOR had a weighted-average interest rate of 2.04% (between 1.23% and 2.91%) at March 31, 2017 and 1.67% (between 0.25% and 2.41%) at December 31, 2016 | Minimum
Debt Instrument
Long-term Debt, Weighted Average Interest Rate	1.23%	1.23%	0.25%
Other Subsidiaries, Excluding MUFG Bank, NA | Secured Debt | Various floating rate nonrecourse borrowings due to BTMU between June 2017 and December 2021. These notes, which bear interest above 1- or 3-month LIBOR had a weighted-average interest rate of 2.04% (between 1.23% and 2.91%) at March 31, 2017 and 1.67% (between 0.25% and 2.41%) at December 31, 2016 | Maximum
Debt Instrument
Long-term Debt, Weighted Average Interest Rate	2.91%	2.91%	2.41%
Other Subsidiaries, Excluding MUFG Bank, NA | Secured Debt | Fixed rate nonrecourse borrowings due December 2026 which had an interest rate of 5.34% at March 31, 2017 and December 31, 2016
Debt Instrument
Long-term debt	$ 38,000,000	$ 38,000,000	$ 39,000,000
Long-term Debt, Weighted Average Interest Rate	5.34%	5.34%	5.34%
Other Subsidiaries, Excluding MUFG Bank, NA | Secured Debt | Various floating rate nonrecourse borrowings due between July 2017 and May 2019. These notes, which bear interest above 1- or 3-month LIBOR had a weighted-average interest rate of 1.87% (between 1.23% and 2.16%) at March 31, 2017 and 2.04% (between 0.85% and 2.73%) at December 31, 2016
Debt Instrument
Long-term debt	$ 394,000,000	$ 394,000,000	$ 398,000,000
Long-term Debt, Weighted Average Interest Rate	1.87%	1.87%	2.04%
Other Subsidiaries, Excluding MUFG Bank, NA | Secured Debt | Various floating rate nonrecourse borrowings due between July 2017 and May 2019. These notes, which bear interest above 1- or 3-month LIBOR had a weighted-average interest rate of 1.87% (between 1.23% and 2.16%) at March 31, 2017 and 2.04% (between 0.85% and 2.73%) at December 31, 2016 | Minimum
Debt Instrument
Long-term Debt, Weighted Average Interest Rate	1.23%	1.23%	0.85%
Other Subsidiaries, Excluding MUFG Bank, NA | Secured Debt | Various floating rate nonrecourse borrowings due between July 2017 and May 2019. These notes, which bear interest above 1- or 3-month LIBOR had a weighted-average interest rate of 1.87% (between 1.23% and 2.16%) at March 31, 2017 and 2.04% (between 0.85% and 2.73%) at December 31, 2016 | Maximum
Debt Instrument
Long-term Debt, Weighted Average Interest Rate	2.16%	2.16%	2.73%
MUFG Americas Holding Corporation | MUFG Union Bank N.A | Senior Debt Obligations [Member] | Floating rate debt due September 2020. This note, which bears interest at 0.85% above 3-month LIBOR, had a rate of 2.00% at March 31, 2017
Debt Instrument
Repayments of debt	$ 3,500,000,000