Derivatives and Hedging Activities - Derivative Instrument Cash Flow Hedge Earning Recognized by Income Statement Location (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Derivatives, Fair Value [Line Items]
Net Gains (Losses) Recognized in OCI	$ 527	$ 106
Net Gains (Losses) Reclassified From OCI Into Income	33	(25)
Interest Income [Member] | Interest Rate [Member] | Cash Flow Hedges [Member]
Derivatives, Fair Value [Line Items]
Net Gains (Losses) Recognized in OCI	562	115
Net Gains (Losses) Reclassified From OCI Into Income	34	(24)
Interest Expense [Member] | Interest Rate [Member] | Cash Flow Hedges [Member]
Derivatives, Fair Value [Line Items]
Net Gains (Losses) Recognized in OCI	(5)	(1)
Net Gains (Losses) Reclassified From OCI Into Income	(1)	(1)
Underwriting Discounts Fees And Commissions [Member] | Interest Rate [Member] | Cash Flow Hedges [Member]
Derivatives, Fair Value [Line Items]
Net Gains (Losses) Recognized in OCI	(30)	(5)
Net Gains (Losses) Reclassified From OCI Into Income	$ 0	0
Other Income [Member] | Foreign Exchange [Member] | Net Investment Hedges [Member]
Derivatives, Fair Value [Line Items]
Net Gains (Losses) Recognized in OCI		(3)
Net Gains (Losses) Reclassified From OCI Into Income		$ 0