Litigation (Details)	1 Months Ended							3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Sep. 30, 2017 asset	Mar. 31, 2017 action	Jan. 31, 2017	Jan. 31, 2015 action	Dec. 31, 2013 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) defendant	Sep. 30, 2017 USD ($)
Loss Contingencies [Line Items]
Legal expense/(benefit)								$ 20,000,000	$ (107,000,000)	$ 90,000,000	$ 172,000,000
Threatened or Pending Litigation | Minimum
Loss Contingencies [Line Items]
Loss contingency range of possible loss	$ 0							0		0
Threatened or Pending Litigation | Maximum
Loss Contingencies [Line Items]
Loss contingency range of possible loss	1,600,000,000							1,600,000,000		$ 1,600,000,000
Foreign Exchange Investigations and Litigation
Loss Contingencies [Line Items]
Exemption of disqualification period					5 years
Disqualification period					10 years
Number of defendants | defendant										1
Number of actions dismissed | action						1
General Motors Litigation
Loss Contingencies [Line Items]
Syndicated term loan facility for General Motors Corporation	1,500,000,000							$ 1,500,000,000		$ 1,500,000,000
Number of representative assets ruled as fixtures | asset			33
Total number of representative assets | asset			40
Interchange Litigation
Loss Contingencies [Line Items]
Number of separate actions | action				2
Settlement amount	36,000,000
Interchange Litigation | The Defendants
Loss Contingencies [Line Items]
Settlement amount	900,000,000						$ 5,300,000,000
Interchange Litigation | Visa Defendants
Loss Contingencies [Line Items]
Settlement amount	600,000,000
Amount deposited into litigation escrow account		$ 600,000,000
Interchange Litigation | Mastercard and Certain Banks
Loss Contingencies [Line Items]
Settlement amount	$ 300,000,000
LIBOR and Other Benchmark Rate Investigations and Litigation | Defendant Banks and ICAP Manipulation of U.S. Dollar ISDAFIX Rates | Pending Litigation
Loss Contingencies [Line Items]
Number of defendants | defendant										1
Municipal Derivatives Litigation | Minimum
Loss Contingencies [Line Items]
Value of warrants the Firm was chosen to underwrite based upon alleged payments made to certain third parties										$ 3,000,000,000.0