Income Taxes - Reconciliation of Expected Income Tax Expense at Federal Statutory Rate of 21 Percent to the Company's Applicable Income Tax Expense (Parenthetical) (Detail) $ in Millions	12 Months Ended
Dec. 31, 2022 USD ($)
Net income tax benefit	$ (79)
MUFG Union Bank [Member]
Net income tax benefit	$ 79

Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations, attributable to increase (decrease) in the income tax rates.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 45
-Paragraph 15
-URI https://asc.fasb.org/extlink&oid=123427490&loc=d3e32059-109318

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 12
-URI https://asc.fasb.org/extlink&oid=121826272&loc=d3e32687-109319

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration