Derivatives and Hedging Activities (Schedule of Impact of the Derivative Instruments on Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Amounts reclassified from OCI into earnings, cash flow hedges	$ (12)	$ 5	$ 6
Interest Expense [Member] | Deposits [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total amounts of income and expense line items presented in the statements of income in which the effects of fair value or cash flow hedges are recorded			(1,238)
Interest Expense [Member] | Deposits [Member] | Designated as Hedges [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total amounts of income and expense line items presented in the statements of income in which the effects of fair value or cash flow hedges are recorded	(1,231)	(1,587)
Interest Expense [Member] | Deposits [Member] | Designated as Hedges [Member] | Interest Rate Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amounts reclassified from OCI into earnings, cash flow hedges	(9)	3	0
Gains (losss) on hedged items, fair value hedges	0	0	0
Gains (losses) on interest rate swap, fair value hedges	0	0	0
Total gains (losses) on fair value hedges	0	0	0
Interest Expense [Member] | Deposits [Member] | Not Designated as Hedges [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) on derivatives not designated as hedges		0	0
Interest Expense [Member] | Long-term Borrowings [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total amounts of income and expense line items presented in the statements of income in which the effects of fair value or cash flow hedges are recorded			(901)
Interest Expense [Member] | Long-term Borrowings [Member] | Designated as Hedges [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total amounts of income and expense line items presented in the statements of income in which the effects of fair value or cash flow hedges are recorded	(602)	(943)
Interest Expense [Member] | Long-term Borrowings [Member] | Designated as Hedges [Member] | Interest Rate Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amounts reclassified from OCI into earnings, cash flow hedges	(3)	2	6
Gains (losss) on hedged items, fair value hedges	(268)	(104)	(18)
Gains (losses) on interest rate swap, fair value hedges	423	72	(23)
Total gains (losses) on fair value hedges	155	(32)	(41)
Interest Expense [Member] | Long-term Borrowings [Member] | Not Designated as Hedges [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) on derivatives not designated as hedges		0	0
Other Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total amounts of income and expense line items presented in the statements of income in which the effects of fair value or cash flow hedges are recorded			97
Other Income [Member] | Designated as Hedges [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total amounts of income and expense line items presented in the statements of income in which the effects of fair value or cash flow hedges are recorded	56	93
Other Income [Member] | Designated as Hedges [Member] | Interest Rate Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amounts reclassified from OCI into earnings, cash flow hedges	0	0	0
Gains (losss) on hedged items, fair value hedges	0	0	0
Gains (losses) on interest rate swap, fair value hedges	0	0	0
Total gains (losses) on fair value hedges	$ 0	0	0
Other Income [Member] | Not Designated as Hedges [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) on derivatives not designated as hedges		$ (1)	$ 1