Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash Flows from Operating Activities:
Net income including noncontrolling interests	$ 1,034	$ 922	$ 599
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
(Reversal of) provision for credit losses	(103)	155	227
Depreciation, amortization and accretion, net	331	325	401
Stock-based compensation—restricted stock units	66	67	54
Deferred income taxes	25	79	(20)
Net gains on sales of securities	(17)	(69)	(20)
Net decrease (increase) in securities borrowed or purchased under resale agreements	(1,147)	11,325	(1,037)
Net increase (decrease) in securities loaned or sold under repurchase agreements	1,821	(4,525)	(915)
Net decrease (increase) in trading account assets	(1,625)	(5,208)	(804)
Net decrease (increase) in other assets	359	(923)	243
Net increase (decrease) in trading account liabilities	695	(807)	2,061
Net increase (decrease) in other liabilities	(137)	(98)	(18)
Loans originated for sale	(813)	(1,358)	(1,294)
Net proceeds from sale of loans originated for sale	697	1,332	1,157
Pension and other benefits adjustment	(169)	(147)	(106)
Other, net	11	15	(16)
Total adjustments	(6)	163	(87)
Net cash provided by (used in) operating activities	1,028	1,085	512
Cash Flows from Investing Activities:
Proceeds from sales of securities available for sale	2,460	4,842	1,985
Proceeds from paydowns and maturities of securities available for sale	2,809	2,171	2,025
Purchases of securities available for sale	(8,912)	(6,666)	(4,768)
Proceeds from paydowns and maturities of securities held to maturity	1,782	2,257	2,682
Purchases of securities held to maturity	(1,360)	(2,447)	(4,511)
Proceeds from sales of loans	926	1,526	1,338
Net decrease (increase) in loans	(2,947)	(519)	(2,130)
Purchases of other investments	(378)	(717)	(640)
Other, net	(60)	148	(122)
Net cash provided by (used in) investing activities	(5,680)	595	(4,141)
Cash Flows from Financing Activities:
Net increase (decrease) in deposits	(2,063)	2,606	(1,750)
Net increase (decrease) in commercial paper and other short-term borrowings	4,709	(1,065)	(1,369)
Capital contribution from MUFG	0	0	200
Proceeds from issuance of long-term debt	5,027	795	6,320
Repayment of long-term debt	(4,801)	(3,082)	(936)
Dividends Paid	(500)	0	0
Other, net	(71)	6	(61)
Change in noncontrolling interests	(10)	6	(4)
Net cash provided by (used in) financing activities	2,291	(734)	2,400
Net change in cash and cash equivalents	(2,361)	946	(1,229)
Cash and cash equivalents at beginning of period	5,753	4,807	6,036
Cash and cash equivalents at end of period	3,392	5,753	4,807
Cash Paid During the Period For:
Interest	919	626	468
Income taxes, net	178	159	157
Supplemental Schedule of Noncash Investing and Financing Activities:
Net transfer of loans held for investment to loans held for sale	776	1,976	1,207
Transfer of assets and liabilities from BTMU and MUFG:
Carrying amount of assets acquired	1,003	0	0
Carrying amount of liabilities assumed	$ 601	$ 0	$ 0