Fair Value Option - Changes in Fair Value Under the Fair Value Option (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
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)	$ 11	$ 7
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)	11	7
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
Securities borrowed
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	37	(27)
Securities borrowed | Principal transactions
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	37	(27)
Securities borrowed | All other income
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	0	0
Debt and equity instruments, excluding loans
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	1,354	(186)
Debt and equity instruments, excluding loans | Principal transactions
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	1,354	(186)
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)	0	0
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)	251	127
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)	248	122
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)	3	5
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)	317	(49)
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)	80	41
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)	237	(90)
Loans: Changes in instrument-specific credit risk
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	5	0
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)	5	0
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
Loans: Other changes in fair value
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	0	(1)
Loans: Other changes in fair value | Principal transactions
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	0	(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	0
Other assets
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	1	(5)
Other assets | Principal transactions
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	1	2
Other assets | All other income
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	0	(7)
Deposits
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	(496)	210
Deposits | Principal transactions
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	(496)	210
Deposits | All other income
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	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)	(5)	10
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)	(5)	10
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
Short-term borrowings
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	(704)	273
Short-term borrowings | Principal transactions
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	(704)	273
Short-term borrowings | 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)	3	(7)
Trading liabilities | Principal transactions
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	3	(7)
Trading liabilities | All other income
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	0	0
Other liabilities
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	(4)	0
Other liabilities | Principal transactions
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	(4)	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)	(2,836)	1,031
Long-term debt | Principal transactions
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	(2,836)	1,031
Long-term debt | All other income
Changes in fair value under the fair value option election
Total nonrecurring fair value gains/(losses)	$ 0	$ 0