Fair Values - Gains (Losses) Due to Changes in Instrument-Specific Credit Risk (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Fair Value disclosure
Cumulative pre-tax DVA gain (loss) recognized in AOCI	$ (532)		$ (532)		$ 172
Borrowings | Trading revenues
Fair Value disclosure
Gains (losses) due to changes in instrument-specific credit risk	(2)	$ (4)	(9)	$ (22)
Borrowings | OCI
Fair Value disclosure
Gains (losses) due to changes in instrument-specific credit risk	442	(1,010)	(702)	425
Loans and other debt | Trading revenues
Fair Value disclosure
Gains (losses) due to changes in instrument-specific credit risk	(3)	55	148	199
Loans and other debt | OCI
Fair Value disclosure
Gains (losses) due to changes in instrument-specific credit risk	0	0	0	0
Lending commitments | Trading revenues
Fair Value disclosure
Gains (losses) due to changes in instrument-specific credit risk	0	(6)	(2)	(3)
Lending commitments | OCI
Fair Value disclosure
Gains (losses) due to changes in instrument-specific credit risk	0	0	0	0
Other | Trading revenues
Fair Value disclosure
Gains (losses) due to changes in instrument-specific credit risk	0	(32)	0	(32)
Other | OCI
Fair Value disclosure
Gains (losses) due to changes in instrument-specific credit risk	$ 1	$ 28	$ (2)	$ 32