Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Cash Flows [Abstract]
Restricted Cash and Cash Equivalents	$ 54	$ 48	$ 136
Cash Flows from Operating Activities:
Net (loss) income including noncontrolling interests	(751)	1,049	1,034
Adjustments to reconcile net (loss) income to net cash provided by (used in) operating activities:
(Reversal of) provision for credit losses	252	106	(103)
Depreciation, amortization and accretion, net	563	411	331
Stock-based compensation—restricted stock units	89	77	66
Deferred income taxes	(264)	(242)	25
Net gains on sales of securities	(39)	(8)	(17)
Net decrease (increase) in securities borrowed or purchased under resale agreements	(1,575)	(1,474)	(1,147)
Net decrease (increase) in securities loaned or sold under repurchase agreements	1,581	848	1,821
Net decrease (increase) in trading account assets	836	(646)	(1,625)
Net decrease (increase) in other assets	216	170	414
Net increase (decrease) in trading account liabilities	(761)	427	695
Net increase (decrease) in other liabilities	219	103	(137)
Loans originated for sale	(3,238)	(2,339)	(813)
Net proceeds from sale of loans originated for sale	2,944	1,626	697
Pension and other benefits adjustment	(42)	(50)	(169)
Goodwill, Impairment Loss	1,614	0	0
Other, net	59	(18)	11
Total adjustments	2,454	(1,009)	49
Net cash provided by (used in) operating activities	1,703	40	1,083
Cash Flows from Investing Activities:
Proceeds from sales of securities available for sale	4,637	1,505	2,460
Proceeds from paydowns and maturities of securities available for sale	2,566	2,822	2,809
Purchases of securities available for sale	(7,839)	(5,643)	(8,912)
Proceeds from paydowns and maturities of securities held to maturity	4,454	1,682	1,782
Purchases of securities held to maturity	(3,153)	(772)	(1,360)
Proceeds from sales of loans	952	770	926
Net decrease (increase) in loans	(2,831)	(6,785)	(2,947)
Purchases of other investments	(143)	(262)	(378)
Other, net	(314)	(57)	(60)
Net cash provided by (used in) investing activities	(1,671)	(6,740)	(5,680)
Cash Flows from Financing Activities:
Net increase (decrease) in deposits	4,880	6,184	(2,063)
Net increase (decrease) in commercial paper and other short-term borrowings	(2,778)	2,198	4,709
Proceeds from issuance of long-term debt	5,698	15,458	5,027
Repayment of long-term debt	(6,471)	(9,655)	(4,801)
Dividends paid	0	0	(500)
Proceeds from (Repurchase of) Equity	0	(2,496)	0
Other, net	(96)	(115)	(71)
Change in noncontrolling interests	32	(4)	(10)
Net cash provided by (used in) financing activities	1,265	11,570	2,291
Net change in cash, cash equivalents and restricted cash	1,297	4,870	(2,306)
Cash, cash equivalents and restricted cash at beginning of period	8,350	3,392
Cash, cash equivalents and restricted cash at end of period	9,641	8,350	3,392
Cash Paid During the Period For:
Interest	2,417	1,761	919
Income taxes, net	202	116	178
Supplemental Schedule of Noncash Investing and Financing Activities:
Net transfer of loans held for investment to (from) loans held for sale	718	44	776
securities held to maturity transferred to securities available for sale	170	0	0
Transfer Of Available For Sale To Held-To-Maturity Securities	0	2,006	0
Transfer of assets and liabilities from BTMU and MUFG:
Carrying amount of assets acquired	0	0	1,003
Carrying amount of liabilities assumed	0	0	601
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 9,695	$ 8,398	$ 3,528