Fair Value Option - Changes in fair value under the fair value option (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Federal funds sold and securities purchased under resale agreements
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	$ (35)	$ (97)	$ (76)
Federal funds sold and securities purchased under resale agreements | Principal transactions
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	(35)	(97)	(76)
Federal funds sold and securities purchased under resale agreements | All other income
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	0	0	0
Securities borrowed
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	22	50	1
Securities borrowed | Principal transactions
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	22	50	1
Securities borrowed | All other income
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	0	0	0
Debt and equity instruments, excluding loans
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	(1,679)	1,945	119
Debt and equity instruments, excluding loans | Principal transactions
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	(1,680)	1,943	120
Debt and equity instruments, excluding loans | All other income
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	1	2	(1)
Loans reported as trading assets: Changes in instrument-specific credit risk
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	415	344	504
Loans reported as trading assets: Changes in instrument-specific credit risk | Principal transactions
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	414	330	461
Loans reported as trading assets: Changes in instrument-specific credit risk | All other income
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	1	14	43
Loans reported as trading assets: Other changes in fair value
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	345	964	763
Loans reported as trading assets: Other changes in fair value | Principal transactions
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	160	217	79
Loans reported as trading assets: Other changes in fair value | All other income
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	185	747	684
Loans: Changes in instrument-specific credit risk
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	(1)	(1)	13
Loans: Changes in instrument-specific credit risk | Principal transactions
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	(1)	(1)	13
Loans: Changes in instrument-specific credit risk | All other income
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	0	0	0
Loans: Other changes in fair value
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	(1)	(9)	(7)
Loans: Other changes in fair value | Principal transactions
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	(1)	(12)	(7)
Loans: Other changes in fair value | All other income
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	0	3	0
Other assets
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	(40)	(44)	82
Other assets | Principal transactions
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	5	11	20
Other assets | All other income
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	(45)	(55)	62
Deposits
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	181	(533)	(134)
Deposits | Principal transactions
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	181	(533)	(134)
Deposits | All other income
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	0	0	0
Federal funds purchased and securities loaned or sold under repurchase agreements
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	11	11	19
Federal funds purchased and securities loaned or sold under repurchase agreements | Principal transactions
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	11	11	19
Federal funds purchased and securities loaned or sold under repurchase agreements | All other income
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	0	0	0
Short-term borrowings
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	862	(747)	(236)
Short-term borrowings | Principal transactions
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	862	(747)	(236)
Short-term borrowings | All other income
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	0	0	0
Trading liabilities
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	1	(1)	6
Trading liabilities | Principal transactions
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	1	(1)	6
Trading liabilities | All other income
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	0	0	0
Beneficial interests issued by consolidated VIEs
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	0	0	23
Beneficial interests issued by consolidated VIEs | Principal transactions
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	0	0	23
Beneficial interests issued by consolidated VIEs | All other income
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	0	0	0
Long-term debt
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	2,695	(2,022)	(773)
Long-term debt | Principal transactions
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	2,695	(2,022)	(773)
Long-term debt | All other income
Changes in fair value under the fair value option election
Fair value option, changes in fair value gain (loss)	$ 0	$ 0	$ 0