Reserves for Credit Losses (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
	Jan. 01, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Reserve for Losses [Roll Forward]
Beginning Balance	$ 2,383			$ 2,383
Provisions		$ 571	$ 604	3,416	$ 1,732
Ending Balance		5,688		5,688
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
Principal write-offs, recoveries		142	135	421	389
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]
Beginning Balance	$ 4,027	5,628	2,168	4,027	2,134
Other		12	(2)	(5)	10
Ending Balance		5,688	2,232	5,688	2,232
Net Write Offs [Member] | Cumulative effect of change in accounting principle - Reserve for Credit Losses, adjusted balance
Reserve for Losses [Roll Forward]
Provisions		571	604	3,416	1,732
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		(432)	(447)	(1,449)	(1,367)
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		(91)	(91)	(301)	(277)
Troubled Debt Restructuring [Member]
Reserve for Losses [Roll Forward]
Net write-offs, principal, interest and fees		(35)	(20)	(98)	(53)
Foreign Currency Translation Adjustments [Member]
Reserve for Losses [Roll Forward]
Other		$ 13	$ (6)	$ (4)	$ (3)