Regulatory Capital Requirements (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Parent [Member]
Regulatory Capital Requirements
Common equity tier 1 capital (to risk-weighted assets), Actual	$ 12,920
Common equity tier 1 capital (to risk-weighted assets), ratio, Actual	13.63%
Common Equity Tier One Risk Based Capital Required for Capital Adequacy	$ 4,265
Common Equity Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets	4.50%
MUFG Americas Holdings Corporation
Regulatory Capital Requirements
Total risk-based capital ratio before application of new methodology	10.00%
Tier 1 capital (to risk-weighted assets), Actual	$ 12,923	$ 12,367
Total capital (to risk-weighted assets), Actual	14,747	14,246
Tier 1 Leverage, Actual	$ 12,923	$ 12,367
Tier 1 capital (to risk-weighted assets), ratio, Actual	13.64%	12.79%
Total capital (to risk-weighted assets), ratio, Actual	15.56%	14.74%
Tier 1 leverage, ratio, Actual	11.40%	11.25%
Tier 1 capital (to risk-weighted assets), Minimum Regulatory Requirement	$ 5,687	$ 3,867
Total capital (to risk-weighted assets), Minimum Regulatory Requirement	7,582	7,733
Tier 1 Leverage, Minimum Regulatory Requirement	$ 4,535	$ 4,396
Tier 1 capital (to risk-weighted assets), ratio, Minimum Regulatory Requirement	6.00%	4.00%
Total capital (to risk-weighted assets), ratio, Minimum Regulatory Requirement	8.00%	8.00%
Tier 1 Leverage, ratio, Minimum Regulatory Requirement	4.00%	4.00%
Bank
Regulatory Capital Requirements
Common equity tier 1 capital (to risk-weighted assets), Actual	$ 12,384	$ 12,087
Tier 1 capital (to risk-weighted assets), Actual	12,384	12,088
Total capital (to risk-weighted assets), Actual	14,003	13,656
Tier 1 Leverage, Actual	$ 12,384	$ 12,088
Common equity tier 1 capital (to risk-weighted assets), ratio, Actual	13.18%	13.09%
Tier 1 capital (to risk-weighted assets), ratio, Actual	13.18%	13.09%
Total capital (to risk-weighted assets), ratio, Actual	14.91%	14.78%
Tier 1 leverage, ratio, Actual	11.03%	11.09%
Common Equity Tier One Risk Based Capital Required for Capital Adequacy	$ 4,227
Tier 1 capital (to risk-weighted assets), Minimum Regulatory Requirement	5,636	$ 5,080
Total capital (to risk-weighted assets), Minimum Regulatory Requirement	7,514	7,389
Tier 1 Leverage, Minimum Regulatory Requirement	$ 4,490	$ 4,361
Common Equity Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets	4.50%
Tier 1 capital (to risk-weighted assets), ratio, Minimum Regulatory Requirement	6.00%	5.50%
Total capital (to risk-weighted assets), ratio, Minimum Regulatory Requirement	8.00%	8.00%
Tier 1 Leverage, ratio, Minimum Regulatory Requirement	4.00%	4.00%
Common Equity Tier One Risk Based Capital Required to be Well Capitalized	$ 6,105
Tier 1 capital (to risk-weighted assets), To Be Well-Capitalized Under Prompt Corrective Action Provisions	7,514	$ 5,542
Total capital (to risk-weighted assets), To Be Well-Capitalized Under Prompt Corrective Action Provisions	9,393	9,237
Tier 1 Leverage, To Be Well-Capitalized Under Prompt Corrective Action Provisions	$ 5,612	$ 5,452
Common Equity Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	6.50%
Tier 1 capital (to risk-weighted assets), ratio, To Be Well-Capitalized Under Prompt Corrective Action Provisions	8.00%	6.00%
Total capital (to risk-weighted assets), ratio, To Be Well-Capitalized Under Prompt Corrective Action Provisions	10.00%	10.00%
Tier 1 Leverage, ratio, To Be Well-Capitalized Under Prompt Corrective Action Provisions	5.00%	5.00%