Litigation (Details)	1 Months Ended					3 Months Ended
	Sep. 30, 2018 USD ($)	Mar. 31, 2017 action	Jan. 31, 2017	Jan. 31, 2015 action	Dec. 31, 2013 USD ($)	Mar. 31, 2019 USD ($) defendant action	Mar. 31, 2018 USD ($)
Loss Contingencies [Line Items]
Legal expense/(benefit)						$ (81,000,000)	$ 70,000,000
Threatened or Pending Litigation | Minimum
Loss Contingencies [Line Items]
Loss contingency range of possible loss						0
Threatened or Pending Litigation | Maximum
Loss Contingencies [Line Items]
Loss contingency range of possible loss						$ 1,400,000,000
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
Interchange Litigation
Loss Contingencies [Line Items]
Number of separate actions | action		2
Interchange Litigation | The Defendants
Loss Contingencies [Line Items]
Settlement amount	$ 900,000,000				$ 5,300,000,000
LIBOR and Other Benchmark Rate Investigations and Litigation | Pending Litigation
Loss Contingencies [Line Items]
Number of putative class actions | action						3