Fair Values - Activity of Level 3 Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - Recurring - Level 3 - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Liabilities at Fair Value
Portion of Unrealized losses (gains) recorded in OCI—Change in net DVA	$ 35	$ (16)	$ 91	$ (119)
Deposits
Liabilities at Fair Value
Beginning balance	99	44	27	47
Realized and unrealized losses (gains)	6	(1)	12	(1)
Issuances	24	5	51	10
Settlements	(4)	0	(4)	(1)
Net transfers	13	(11)	52	(18)
Ending balance	138	37	138	37
Unrealized losses (gains)	6	(1)	12	(1)
Nonderivative trading liabilities
Liabilities at Fair Value
Beginning balance	43	39	16	25
Realized and unrealized losses (gains)	(9)	(3)	(10)	(6)
Purchases	(24)	(17)	(30)	(19)
Sales	11	7	28	22
Net transfers	15	(1)	32	3
Ending balance	36	25	36	25
Unrealized losses (gains)	(9)	(2)	(10)	(4)
Securities sold under agreements to repurchase
Liabilities at Fair Value
Beginning balance	0	0	0	150
Net transfers	0	0	0	(150)
Ending balance	0	0	0	0
Unrealized losses (gains)	0	0	0	0
Other secured financings
Liabilities at Fair Value
Beginning balance	153	220	208	239
Realized and unrealized losses (gains)	2	(5)	6	(17)
Issuances	0	4	0	7
Settlements	(1)	(8)	(8)	(18)
Net transfers	0	(41)	(52)	(41)
Ending balance	154	170	154	170
Unrealized losses (gains)	2	(5)	6	(17)
Borrowings
Liabilities at Fair Value
Beginning balance	3,775	3,626	3,806	2,984
Realized and unrealized losses (gains)	172	(130)	444	(201)
Issuances	354	306	598	825
Settlements	(99)	(141)	(243)	(195)
Net transfers	(263)	(366)	(666)	(118)
Ending balance	3,939	3,295	3,939	3,295
Unrealized losses (gains)	173	(133)	419	(199)
Interest rate
Assets at Fair value
Beginning balance	551	670	618	1,218
Realized and unrealized gains (losses)	238	(75)	183	(1)
Purchases	53	61	59	69
Issuances	(19)	(24)	(30)	(51)
Settlements	(1)	(45)	(15)	(131)
Net transfers	(6)	(20)	1	(537)
Ending balance	816	567	816	567
Unrealized gains (losses)	230	(99)	234	(13)
Credit
Assets at Fair value
Beginning balance	(261)	(30)	40	41
Realized and unrealized gains (losses)	30	111	217	(22)
Purchases	28	15	93	4
Issuances	(19)	(41)	(470)	(40)
Settlements	39	(57)	(8)	17
Net transfers	45	0	(10)	(2)
Ending balance	(138)	(2)	(138)	(2)
Unrealized gains (losses)	30	115	224	(28)
Foreign exchange
Assets at Fair value
Beginning balance	5	(33)	75	(112)
Realized and unrealized gains (losses)	(33)	37	(154)	96
Purchases	0	0	0	0
Issuances	0	(19)	0	(46)
Settlements	(22)	(3)	(12)	46
Net transfers	21	(8)	62	(10)
Ending balance	(29)	(26)	(29)	(26)
Unrealized gains (losses)	(37)	43	(45)	28
Equity
Assets at Fair value
Beginning balance	(1,760)	1,015	(1,485)	1,208
Realized and unrealized gains (losses)	86	51	(92)	163
Purchases	60	29	96	94
Issuances	(158)	(191)	(359)	(930)
Settlements	43	185	185	294
Net transfers	14	(2,624)	(60)	(2,364)
Ending balance	(1,715)	(1,535)	(1,715)	(1,535)
Unrealized gains (losses)	70	(14)	(106)	135
Commodity and other
Assets at Fair value
Beginning balance	2,106	1,660	2,052	1,446
Realized and unrealized gains (losses)	(145)	170	(113)	392
Purchases	8	1	16	35
Issuances	(2)	(3)	(17)	(6)
Settlements	(106)	122	(183)	7
Net transfers	0	82	106	158
Ending balance	1,861	2,032	1,861	2,032
Unrealized gains (losses)	(272)	107	(306)	230
U.S. Treasury and agency securities
Assets at Fair value
Beginning balance	7	0	54	0
Purchases	5	0	5	0
Sales	(4)	0	(54)	0
Net transfers	(3)	0	0	0
Ending balance	5	0	5	0
Unrealized gains (losses)	0	0	0	0
Other sovereign government obligations
Assets at Fair value
Beginning balance	5	7	17	1
Realized and unrealized gains (losses)	0	(3)	0	0
Purchases	8	2	8	4
Sales	(3)	(1)	(4)	0
Net transfers	0	0	(11)	0
Ending balance	10	5	10	5
Unrealized gains (losses)	0	0	0	0
State and municipal securities
Assets at Fair value
Beginning balance	12	2	148	8
Realized and unrealized gains (losses)	0	0	0	0
Purchases	15	1	15	1
Sales	(11)	(1)	(43)	(7)
Net transfers	0	0	(104)	0
Ending balance	16	2	16	2
Unrealized gains (losses)	0	0	0	0
MABS
Assets at Fair value
Beginning balance	301	342	354	423
Realized and unrealized gains (losses)	(5)	0	3	76
Purchases	52	35	63	74
Sales	(43)	(88)	(133)	(282)
Settlements	(19)	(7)	(22)	(12)
Net transfers	194	45	215	48
Ending balance	480	327	480	327
Unrealized gains (losses)	(12)	(6)	(24)	0
Loans and lending commitments
Assets at Fair value
Beginning balance	6,343	8,128	6,870	5,945
Realized and unrealized gains (losses)	73	(62)	44	(6)
Purchases	957	1,726	1,548	3,841
Sales	(1,021)	(615)	(588)	(913)
Settlements	(733)	(1,781)	(1,487)	(1,531)
Net transfers	(15)	(473)	(783)	(413)
Ending balance	5,604	6,923	5,604	6,923
Unrealized gains (losses)	66	(78)	44	(61)
Corporate and other debt
Assets at Fair value
Beginning balance	1,061	814	1,076	701
Realized and unrealized gains (losses)	86	37	161	43
Purchases	407	166	428	366
Sales	(101)	(194)	(267)	(165)
Settlements	(3)	(3)	(5)	(1)
Net transfers	(86)	(119)	(29)	(243)
Ending balance	1,364	701	1,364	701
Unrealized gains (losses)	85	5	152	6
Corporate equities
Assets at Fair value
Beginning balance	152	233	95	166
Realized and unrealized gains (losses)	(12)	(4)	(10)	2
Purchases	21	21	28	43
Sales	(13)	(25)	(31)	(49)
Net transfers	(50)	(54)	16	9
Ending balance	98	171	98	171
Unrealized gains (losses)	(10)	(3)	(7)	(7)
Investments
Assets at Fair value
Beginning balance	974	1,012	757	1,020
Realized and unrealized gains (losses)	26	(8)	38	23
Purchases	9	17	14	64
Sales	(32)	(28)	(36)	(133)
Net transfers	(192)	(52)	12	(33)
Ending balance	785	941	785	941
Unrealized gains (losses)	$ 29	$ 2	$ 38	$ 7