Litigation (Details)	1 Months Ended				2 Months Ended	3 Months Ended		6 Months Ended
	Sep. 30, 2018 USD ($)	Mar. 31, 2017 action	Jan. 31, 2017	Dec. 31, 2013 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) action	Jun. 30, 2018 USD ($)
Loss Contingencies [Line Items]
Legal expense/(benefit)						$ 69,000,000	$ 0	$ (12,000,000)	$ 70,000,000
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					1,300,000,000	1,300,000,000		$ 1,300,000,000
Foreign Exchange Investigations and Litigation
Loss Contingencies [Line Items]
Exemption of disqualification period			5 years
Disqualification period			10 years
Settlement amount					265,000,000
Number of actions dismissed | action								2
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
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