Allowance for Losses on Financial Assets Allowance for Losses on Financial Assets (Narrative) (Details) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Jun. 30, 2020	Jan. 01, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Allowance for Losses on Financial Assets [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ (11,553)	$ (11,382)		$ (8,300)	$ (3,809)	$ (4,943)	$ 410
Allowance for Credit Loss	711		$ 337
Retained Earnings
Allowance for Losses on Financial Assets [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ 47,029	$ 47,478		$ 50,644	$ 53,986	$ 52,819	$ 55,941
Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-13
Allowance for Losses on Financial Assets [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			(162)
Cumulative Effect, Period of Adoption, Adjustment | Retained Earnings | Accounting Standards Update 2016-13
Allowance for Losses on Financial Assets [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			$ (162)