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		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Liabilities at Fair Value
Portion of Unrealized losses (gains) recorded in OCI—Change in net DVA	$ (23)	$ 82	$ 68	$ (45)
Deposits
Liabilities at Fair Value
Beginning balance	138	37	27	47
Realized and unrealized losses (gains)	5	2	16	(1)
Issuances	23	11	70	27
Settlements	(8)	0	(12)	(2)
Net transfers	(13)	23	44	2
Ending balance	145	73	145	73
Unrealized losses (gains)	5	2	16	(1)
Nonderivative trading liabilities
Liabilities at Fair Value
Beginning balance	36	25	16	25
Realized and unrealized losses (gains)	(7)	0	(37)	(4)
Purchases	(13)	(12)	(31)	(15)
Sales	6	3	36	12
Net transfers	18	(2)	56	(4)
Ending balance	40	14	40	14
Unrealized losses (gains)	(7)	0	(37)	(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	154	170	208	239
Realized and unrealized losses (gains)	(1)	2	5	(16)
Issuances	0	0	0	8
Settlements	0	0	(8)	(18)
Net transfers	(43)	0	(95)	(41)
Ending balance	110	172	110	172
Unrealized losses (gains)	(1)	2	5	(16)
Borrowings
Liabilities at Fair Value
Beginning balance	3,939	3,295	3,806	2,984
Realized and unrealized losses (gains)	88	56	498	(156)
Issuances	201	344	610	1,275
Settlements	(260)	(81)	(438)	(339)
Net transfers	(430)	6	(938)	(144)
Ending balance	3,538	3,620	3,538	3,620
Unrealized losses (gains)	91	55	459	(168)
Interest rate
Assets at Fair value
Beginning balance	816	567	618	1,218
Realized and unrealized gains (losses)	(40)	(3)	143	(46)
Purchases	69	12	132	84
Issuances	(11)	(9)	(22)	(38)
Settlements	2	(2)	16	(92)
Net transfers	(48)	12	(99)	(549)
Ending balance	788	577	788	577
Unrealized gains (losses)	120	24	214	(47)
Credit
Assets at Fair value
Beginning balance	(138)	(2)	40	41
Realized and unrealized gains (losses)	(183)	(39)	36	(17)
Purchases	44	4	103	9
Issuances	(19)	0	(162)	(40)
Settlements	389	58	90	30
Net transfers	12	0	(2)	(2)
Ending balance	105	21	105	21
Unrealized gains (losses)	20	(41)	41	(20)
Foreign exchange
Assets at Fair value
Beginning balance	(29)	(26)	75	(112)
Realized and unrealized gains (losses)	67	(35)	(83)	71
Purchases	0	0	0	2
Issuances	0	0	0	(48)
Settlements	5	2	0	43
Net transfers	9	15	60	0
Ending balance	52	(44)	52	(44)
Unrealized gains (losses)	79	(9)	26	1
Equity
Assets at Fair value
Beginning balance	(1,715)	(1,535)	(1,485)	1,208
Realized and unrealized gains (losses)	(61)	(149)	59	83
Purchases	36	29	75	120
Issuances	(207)	(138)	(227)	(1,052)
Settlements	(56)	84	(173)	319
Net transfers	622	38	370	(2,349)
Ending balance	(1,381)	(1,671)	(1,381)	(1,671)
Unrealized gains (losses)	(86)	(132)	81	19
Commodity and other
Assets at Fair value
Beginning balance	1,861	2,032	2,052	1,446
Realized and unrealized gains (losses)	120	(29)	35	332
Purchases	126	0	145	80
Issuances	(36)	(11)	(71)	(18)
Settlements	(107)	(1)	(307)	17
Net transfers	10	29	120	163
Ending balance	1,974	2,020	1,974	2,020
Unrealized gains (losses)	33	(105)	(89)	33
U.S. Treasury and agency securities
Assets at Fair value
Beginning balance	5	0	54	0
Purchases	11	5	18	5
Sales	0	0	(54)	0
Net transfers	2	0	0	0
Ending balance	18	5	18	5
Unrealized gains (losses)	0	0	0	0
Other sovereign government obligations
Assets at Fair value
Beginning balance	10	5	17	1
Realized and unrealized gains (losses)	(3)	0	(2)	0
Purchases	2	32	13	35
Sales	(2)	(2)	(6)	0
Settlements	0	0	0	0
Net transfers	5	1	(10)	0
Ending balance	12	36	12	36
Unrealized gains (losses)	(3)	0	(2)	0
State and municipal securities
Assets at Fair value
Beginning balance	16	2	148	8
Realized and unrealized gains (losses)	0	0	0	0
Purchases	0	2	0	3
Sales	(2)	0	(43)	(7)
Net transfers	(13)	0	(104)	0
Ending balance	1	4	1	4
Unrealized gains (losses)	0	0	0	0
MABS
Assets at Fair value
Beginning balance	480	327	354	423
Realized and unrealized gains (losses)	(10)	(1)	(9)	88
Purchases	5	23	66	73
Sales	(58)	(46)	(157)	(317)
Settlements	0	(14)	(39)	(16)
Net transfers	(16)	27	186	65
Ending balance	401	316	401	316
Unrealized gains (losses)	(8)	(8)	(38)	(6)
Loans and lending commitments
Assets at Fair value
Beginning balance	5,604	6,923	6,870	5,945
Realized and unrealized gains (losses)	(51)	17	3	16
Purchases	852	2,076	1,934	4,030
Sales	(464)	(1,184)	(1,541)	(978)
Settlements	(811)	(777)	(2,130)	(1,926)
Net transfers	(261)	(320)	(267)	(352)
Ending balance	4,869	6,735	4,869	6,735
Unrealized gains (losses)	(55)	12	283	(8)
Corporate and other debt
Assets at Fair value
Beginning balance	1,364	701	1,076	701
Realized and unrealized gains (losses)	157	(4)	269	51
Purchases	341	109	632	276
Sales	(474)	(153)	(587)	(227)
Settlements	0	(6)	(7)	(8)
Net transfers	2	63	7	(83)
Ending balance	1,390	710	1,390	710
Unrealized gains (losses)	114	9	217	16
Corporate equities
Assets at Fair value
Beginning balance	98	171	95	166
Realized and unrealized gains (losses)	1	(7)	(41)	17
Purchases	5	15	44	69
Sales	(16)	(50)	(268)	(134)
Net transfers	15	(23)	273	(12)
Ending balance	103	106	103	106
Unrealized gains (losses)	7	5	(38)	14
Investments
Assets at Fair value
Beginning balance	785	941	757	1,020
Realized and unrealized gains (losses)	(15)	5	19	5
Purchases	7	72	28	134
Sales	(7)	(103)	(43)	(209)
Net transfers	15	(97)	24	(132)
Ending balance	785	818	785	818
Unrealized gains (losses)	$ (12)	$ 2	$ 22	$ 5