Derivative Instruments And Hedging Activities (Narrative) (Details) - USD ($)	3 Months Ended			9 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Fair value hedge swap portfolio		$ 3,600,000,000		$ 3,600,000,000
Common Stock and Additional Paid-in Capital		3,000,000,000.0		3,000,000,000.0
Cash collateral pledged for derivative liabilities		102,000,000		102,000,000
Derivative Instruments, Gain Reclassified from Accumulated OCI into Income, Effective Portion				12,000,000
Change In Fair Value Of Derivative Asset By Credit Value Adjustment		(17,000,000)	$ (1,000,000)	(17,000,000)	$ (1,000,000)	$ (3,000,000)
Derivative Credit Risk Valuation Adjustment, Derivative Liabilities		0	$ 2,000,000	0	$ 2,000,000
Floors Purchased as Hedging Instruments		9,000,000		9,000,000
Additional collateral that would be required to be pledge if credit rating was downgraded by one notch		2,000,000		$ 2,000,000
Debt Instrument, Interest Rate Terms				3.35%
Subordinated Debt		$ 87,000,000		$ 87,000,000		87,000,000
Types of Items Hedged by Interest Rate Derivatives		$1	$—	$19	$—
Fair Value Hedge Swap Portfolio, Change		$ 1,000,000
Subsequent Event [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Debt Instrument, Interest Rate Terms	3.25%
Subordinated Debt	$ 500,000,000
Derivatives Designated As Hedging Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Notional Amount		4,613,000,000		$ 4,613,000,000		1,187,000,000
Derivative Financial Instruments, Liabilities [Member] | Other Liabilities [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gross amounts recognized		16,000,000		16,000,000		39,000,000
Fair Value Hedging [Member] | Interest Rate Swap [Member] | Derivatives Designated As Hedging Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Notional Amount		1,000,000,000		1,000,000,000		500,000,000
Cash Flow Hedging [Member] | Interest Rate Floor [Member] | Derivatives Designated As Hedging Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Notional Amount		0		0		0
Cash Flow Hedging [Member] | Interest Rate Swap [Member] | Derivatives Designated As Hedging Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Notional Amount		$ 3,613,000,000		$ 3,613,000,000		$ 687,000,000