Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Cash Flows [Abstract]
Restricted Cash and Cash Equivalents	$ 48	$ 136	$ 81
Cash Flows from Operating Activities:
Net income including noncontrolling interests	1,049	1,034	922
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
(Reversal of) provision for credit losses	106	(103)	155
Depreciation, amortization and accretion, net	411	331	325
Stock-based compensation—restricted stock units	77	66	67
Deferred income taxes	(242)	25	79
Net gains on sales of securities	(8)	(17)	(69)
Net decrease (increase) in securities borrowed or purchased under resale agreements	(1,474)	(1,147)	11,325
Net increase (decrease) in securities loaned or sold under repurchase agreements	848	1,821	(4,525)
Net decrease (increase) in trading account assets	(646)	(1,625)	(5,208)
Net decrease (increase) in other assets	170	414	(875)
Net increase (decrease) in trading account liabilities	427	695	(807)
Net increase (decrease) in other liabilities	103	(137)	(98)
Loans originated for sale	(2,339)	(813)	(1,358)
Net proceeds from sale of loans originated for sale	1,626	697	1,332
Pension and other benefits adjustment	(50)	(169)	(147)
Other, net	(18)	11	15
Total adjustments	(1,009)	49	211
Net cash provided by (used in) operating activities	40	1,083	1,133
Cash Flows from Investing Activities:
Proceeds from sales of securities available for sale	1,505	2,460	4,842
Proceeds from paydowns and maturities of securities available for sale	2,822	2,809	2,171
Purchases of securities available for sale	(5,643)	(8,912)	(6,666)
Proceeds from paydowns and maturities of securities held to maturity	1,682	1,782	2,257
Purchases of securities held to maturity	(772)	(1,360)	(2,447)
Proceeds from sales of loans	770	926	1,526
Net decrease (increase) in loans	(6,785)	(2,947)	(519)
Purchases of other investments	(262)	(378)	(717)
Other, net	(57)	(60)	148
Net cash provided by (used in) investing activities	(6,740)	(5,680)	595
Cash Flows from Financing Activities:
Net increase (decrease) in deposits	6,184	(2,063)	2,606
Net increase (decrease) in commercial paper and other short-term borrowings	2,198	4,709	(1,065)
Proceeds from issuance of long-term debt	15,458	5,027	795
Repayment of long-term debt	(9,655)	(4,801)	(3,082)
Dividends paid	0	(500)	0
Proceeds from (Repurchase of) Equity	(2,496)	0	0
Other, net	(115)	(71)	6
Change in noncontrolling interests	(4)	(10)	6
Net cash provided by (used in) financing activities	11,570	2,291	(734)
Net change in cash and cash equivalents	4,870	(2,306)	994
Cash, cash equivalents and restricted cash at beginning of period	3,392	5,753
Cash, cash equivalents and restricted cash at end of period	8,350	3,392	5,753
Cash Paid During the Period For:
Interest	1,761	919	626
Income taxes, net	116	178	159
Supplemental Schedule of Noncash Investing and Financing Activities:
Net transfer of loans held for investment to loans held for sale	44	776	1,976
Transfer Of Available For Sale To Held-To-Maturity Securities	2,006	0	0
Transfer of assets and liabilities from BTMU and MUFG:
Carrying amount of assets acquired	0	1,003	0
Carrying amount of liabilities assumed	0	601	0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 8,398	$ 3,528	$ 5,834