Reserves for Credit Losses (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Jan. 01, 2020
Reserve for Losses [Roll Forward]
Balance, January 1	$ 2,383
Provisions	1,876	$ 525
Net write-offs, principal, interest and fees	(145)	(124)
Balance, March 31	5,236
Accounting Standards Update 2016-13 [Member]
Reserve for Losses [Roll Forward]
Balance, January 1	4,027	2,134
Other	(42)	11
Balance, March 31	5,236	2,121
Increase related to adoption of the CECL methodology			$ 1,643
Net Write Offs [Member] | Accounting Standards Update 2016-13 [Member]
Reserve for Losses [Roll Forward]
Provisions	1,876	525
Principal [Member] | Accounting Standards Update 2016-13 [Member]
Reserve for Losses [Roll Forward]
Net write-offs, principal, interest and fees	(518)	(457)
Interest and Fees [Member] | Accounting Standards Update 2016-13 [Member]
Reserve for Losses [Roll Forward]
Net write-offs, principal, interest and fees	(107)	(92)
Troubled Debt Restructuring [Member]
Reserve for Losses [Roll Forward]
Net write-offs, principal, interest and fees	(31)	(15)
Foreign Currency Translation Adjustments [Member]
Reserve for Losses [Roll Forward]
Other	$ (42)	$ 6