Reserves for Credit Losses (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
	Jan. 01, 2020	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Reserve for Losses [Roll Forward]
Balance, January 1	$ 2,383			$ 2,383
Provisions		$ 969	$ 603	2,845	$ 1,128
Balance, June 30		5,628		5,628
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
Principal write-offs, recoveries				279	254
Cumulative effect of change in accounting principle - Reserve for Credit Losses
Reserve for Losses [Roll Forward]
Increase related to adoption of the CECL methodology	$ 1,643
Cumulative effect of change in accounting principle - Reserve for Credit Losses, adjusted balance
Reserve for Losses [Roll Forward]
Balance, January 1	$ 4,027			4,027	2,134
Other				(17)	12
Balance, June 30		$ 5,628	$ 2,168	5,628	2,168
Net Write Offs [Member] | Cumulative effect of change in accounting principle - Reserve for Credit Losses, adjusted balance
Reserve for Losses [Roll Forward]
Provisions				2,845	1,128
Principal [Member] | Cumulative effect of change in accounting principle - Reserve for Credit Losses, adjusted balance
Reserve for Losses [Roll Forward]
Net write-offs, principal, interest and fees				(1,017)	(920)
Interest and Fees [Member] | Cumulative effect of change in accounting principle - Reserve for Credit Losses, adjusted balance
Reserve for Losses [Roll Forward]
Net write-offs, principal, interest and fees				(210)	(186)
Troubled Debt Restructuring [Member]
Reserve for Losses [Roll Forward]
Net write-offs, principal, interest and fees				(63)	(33)
Foreign Currency Translation Adjustments [Member]
Reserve for Losses [Roll Forward]
Other				$ (17)	$ 3