Derivative Instruments And Hedging Activities (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended			12 Months Ended
	Sep. 30, 2017		Sep. 30, 2016		Sep. 30, 2017		Sep. 30, 2016	Sep. 30, 2018	Dec. 31, 2016
Derivative [Line Items]
Derivative Instruments, Gain Reclassified from Accumulated OCI into Income, Effective Portion								$ 2
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	$ 0		$ (5)		$ 0		$ 23
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	0		3		3		9
Fair values of derivative assets reduced (increased) by net credit valuation adjustments	4		7		4		7
Total derivatives, Notional amount	6,221				6,221				$ 6,209
Cash collateral pledged for derivative liabilities	46				46
Additional collateral that would be required to be pledge if credit rating was downgraded by one notch	1				1
Derivative Instrument, Noninterest Income (Expense)	8		8		19		16
Derivatives Designated As Hedging Instrument Offset To Interest Expense	0		0		0		0
Derivative Credit Risk Valuation Adjustment, Derivative Liabilities	1				1				0
Derivatives Designated As Hedging Instruments [Member] | Cash Flow Hedging [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	0		(5)		0		23
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	0	[1]	3	[1]	3	[1]	9
Total derivatives, Notional amount	1,138				1,138				1,388
Derivatives Not Designated As Hedging Instruments [Member]
Derivative [Line Items]
Total derivatives, Notional amount	5,083				5,083				4,821
Derivatives Not Designated As Hedging Instruments [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Total derivatives, Notional amount	205				205				235
Derivative Instrument, Noninterest Income (Expense)	0		1		(1)		3
Derivatives Not Designated As Hedging Instruments [Member] | Interest Rate Swaps For Customers [Member]
Derivative [Line Items]
Total derivatives, Notional amount	4,598				4,598				4,162
Derivative Instrument, Noninterest Income (Expense)	4		4		8		5
Derivatives Not Designated As Hedging Instruments [Member] | Foreign Exchange [Member]
Derivative [Line Items]
Total derivatives, Notional amount	280				280				424
Derivative Instrument, Noninterest Income (Expense)	4		$ 3		12		$ 8
Other Liabilities [Member]
Derivative [Line Items]
Derivative Liability, Fair Value, Gross Liability	35				35				59
Other Liabilities [Member] | Derivatives Designated As Hedging Instruments [Member] | Cash Flow Hedging [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative Liability, Fair Value, Gross Liability	0				0				1
Other Liabilities [Member] | Derivatives Not Designated As Hedging Instruments [Member]
Derivative [Line Items]
Derivative Liability, Fair Value, Gross Liability	35				35				58
Other Liabilities [Member] | Derivatives Not Designated As Hedging Instruments [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative Liability, Fair Value, Gross Liability	0				0				0
Other Liabilities [Member] | Derivatives Not Designated As Hedging Instruments [Member] | Interest Rate Swaps For Customers [Member]
Derivative [Line Items]
Derivative Liability, Fair Value, Gross Liability	30				30				49
Other Liabilities [Member] | Derivatives Not Designated As Hedging Instruments [Member] | Foreign Exchange [Member]
Derivative [Line Items]
Derivative Liability, Fair Value, Gross Liability	5				5				9
Other Liabilities [Member] | Derivative Financial Instruments, Liabilities [Member]
Derivative [Line Items]
Gross amounts recognized	$ 35				$ 35				$ 59

[1] Amounts recognized in OCI and reclassified from AOCI represent the effective portion of the derivative gain (loss). For the 12 months following September 30, 2017, we estimate that $2 million will be reclassified from AOCI into interest income.