Derivatives and Hedging Activities - Derivative Instrument Cash Flow Hedge Earning Recognized by Income Statement Location (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Derivatives, Fair Value [Line Items]
Net Gains (Losses) Recognized in OCI	$ 55	$ 71	$ (135)	$ 598
Net Gains (Losses) Reclassified From OCI Into Income	83	(89)	172	122
Interest income – loans | Interest rate | Cash Flow Hedges
Derivatives, Fair Value [Line Items]
Net Gains (Losses) Recognized in OCI	61	62	(142)	624
Net Gains (Losses) Reclassified From OCI Into Income	85	90	173	124
Interest expense — Long-term debt | Interest rate | Cash Flow Hedges
Derivatives, Fair Value [Line Items]
Net Gains (Losses) Recognized in OCI	(2)	(1)	2	(6)
Net Gains (Losses) Reclassified From OCI Into Income	(1)	(1)	(2)	(2)
Investment banking and debt placement fees | Interest rate | Cash Flow Hedges
Derivatives, Fair Value [Line Items]
Net Gains (Losses) Recognized in OCI	(4)	10	5	(20)
Net Gains (Losses) Reclassified From OCI Into Income	$ (1)	$ 0	1	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