Fair Value Option - Changes in Fair Value Under the Fair Value Option (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Federal funds sold and securities purchased under resale agreements
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	$ (33)	$ (12)	$ (26)	$ (33)
Federal funds sold and securities purchased under resale agreements | Principal transactions
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	(33)	(12)	(26)	(33)
Federal funds sold and securities purchased under resale agreements | All other income
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	0	0	0	0
Securities borrowed
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	29	13	2	90
Securities borrowed | Principal transactions
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	29	13	2	90
Securities borrowed | All other income
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	0	0	0	0
Debt and equity instruments, excluding loans
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	(258)	336	(444)	697
Debt and equity instruments, excluding loans | Principal transactions
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	(259)	334	(445)	695
Debt and equity instruments, excluding loans | All other income
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	1	2	1	2
Loans reported as trading assets: Changes in instrument-specific credit risk
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	213	78	340	258
Loans reported as trading assets: Changes in instrument-specific credit risk | Principal transactions
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	214	69	336	243
Loans reported as trading assets: Changes in instrument-specific credit risk | All other income
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	(1)	9	4	15
Loans reported as trading assets: Other changes in fair value
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	94	272	45	429
Loans reported as trading assets: Other changes in fair value | Principal transactions
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	29	43	70	77
Loans reported as trading assets: Other changes in fair value | All other income
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	65	229	(25)	352
Loans: Changes in instrument-specific credit risk
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	(1)	0	(1)	(1)
Loans: Changes in instrument-specific credit risk | Principal transactions
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	(1)	0	(1)	(1)
Loans: Changes in instrument-specific credit risk | All other income
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	0	0	0	0
Loans: Other changes in fair value
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	(1)	4	(2)	4
Loans: Other changes in fair value | Principal transactions
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	(1)	1	(2)	1
Loans: Other changes in fair value | All other income
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	0	3	0	3
Other assets
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	(3)	(13)	(8)	(15)
Other assets | Principal transactions
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	0	3	2	7
Other assets | All other income
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	(3)	(16)	(10)	(22)
Deposits
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	129	(86)	339	(245)
Deposits | Principal transactions
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	129	(86)	339	(245)
Deposits | All other income
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	0	0	0	0
Federal funds purchased and securities loaned or sold under repurchase agreements
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	9	(3)	19	2
Federal funds purchased and securities loaned or sold under repurchase agreements | Principal transactions
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	9	(3)	19	2
Federal funds purchased and securities loaned or sold under repurchase agreements | All other income
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	0	0	0	0
Short-term borrowings
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	(162)	43
Short-term borrowings | Principal transactions
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	(162)	43
Short-term borrowings | All other income
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	0	0
Other borrowed funds
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)			111	(431)
Other borrowed funds | Principal transactions
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)			111	(431)
Other borrowed funds | All other income
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)			0	0
Trading liabilities
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	6	0	(1)	(1)
Trading liabilities | Principal transactions
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	6	0	(1)	(1)
Trading liabilities | All other income
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	0	0	0	0
Beneficial interests issued by consolidated VIEs
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	0	0	0	0
Beneficial interests issued by consolidated VIEs | Principal transactions
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	0	0	0	0
Beneficial interests issued by consolidated VIEs | All other income
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	0	0	0	0
Other liabilities
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)			0	0
Other liabilities | Principal transactions
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)			0	0
Other liabilities | All other income
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)			0	0
Long-term debt
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	196	(170)	1,227	(923)
Long-term debt | Principal transactions
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	196	(170)	1,227	(923)
Long-term debt | All other income
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	$ 0	$ 0	$ 0	$ 0