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, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Derivatives, Fair Value [Line Items]
Net Gains (Losses) Recognized in OCI	$ 2	$ 15	$ (133)	$ 613
Net Gains (Losses) Reclassified From OCI Into Income	77	99	250	221
Interest income – loans | Interest rate | Cash Flow Hedges
Derivatives, Fair Value [Line Items]
Net Gains (Losses) Recognized in OCI	(2)	5	(144)	629
Net Gains (Losses) Reclassified From OCI Into Income	79	100	253	224
Interest expense — Long-term debt | Interest rate | Cash Flow Hedges
Derivatives, Fair Value [Line Items]
Net Gains (Losses) Recognized in OCI	0	0	2	(6)
Net Gains (Losses) Reclassified From OCI Into Income	(1)	(1)	(3)	(3)
Investment banking and debt placement fees | Interest rate | Cash Flow Hedges
Derivatives, Fair Value [Line Items]
Net Gains (Losses) Recognized in OCI	4	10	9	(10)
Net Gains (Losses) Reclassified From OCI Into Income	$ (1)	$ 0	0	0
Other income | Foreign exchange | Net Investment Hedges
Derivatives, Fair Value [Line Items]
Net Gains (Losses) Recognized in OCI			0	0
Net Gains (Losses) Reclassified From OCI Into Income			$ 0	$ 0