Derivatives and Hedging Activities - Derivative Instrument Cash Flow Hedge Earning Recognized by Income Statement Location (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Derivatives, Fair Value [Line Items]
Net Gains (Losses) Recognized in OCI	$ 15	$ 81	$ 613	$ 453
Net Gains (Losses) Reclassified From OCI Into Income	99	(9)	221	(53)
Interest income – loans | Interest rate | Cash Flow Hedges
Derivatives, Fair Value [Line Items]
Net Gains (Losses) Recognized in OCI	5	86	629	471
Net Gains (Losses) Reclassified From OCI Into Income	100	(8)	224	(51)
Interest expense — Long-term debt | Interest rate | Cash Flow Hedges
Derivatives, Fair Value [Line Items]
Net Gains (Losses) Recognized in OCI	0	(2)	(6)	(5)
Net Gains (Losses) Reclassified From OCI Into Income	(1)	(1)	(3)	(2)
Investment banking and debt placement fees | Interest rate | Cash Flow Hedges
Derivatives, Fair Value [Line Items]
Net Gains (Losses) Recognized in OCI	10	(4)	(10)	(10)
Net Gains (Losses) Reclassified From OCI Into Income	$ 0	0	0	0
Other income | Foreign exchange | Net Investment Hedges
Derivatives, Fair Value [Line Items]
Net Gains (Losses) Recognized in OCI		1	0	(3)
Net Gains (Losses) Reclassified From OCI Into Income		$ 0	$ 0	$ 0