Loans And Allowance For Credit Losses (Narrative) (Details) $ in Millions		3 Months Ended		6 Months Ended		12 Months Ended
		Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) d	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jun. 30, 2016 USD ($)
Loans And Allowance For Credit Losses [Line Items]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Provision for Loan Losses		$ 0	$ 1	$ 0	$ 1
Unfunded Lending Commitments on Troubled Debt Restructuring		21		21		$ 21	$ 14
Loans and Leases Receivable, Gross		43,683		43,683		43,683	42,649
Financing Receivable, Recorded Investment, Current		43,418		43,418		43,418	42,340
Financing Receivable, Modifications, Subsequent Default, Recorded Investment		3	19	3	21	123		$ 162
Unearned income and fees, net of related costs		71		71		71	77
Owner occupied and commercial real estate loans, unamortized premiums		17		17		17	20
Land Development Loans		241		241		241	290
Loans at carrying value pledged as collateral for current and potential borrowings		24,600		24,600		24,600	24,000
Payments for Origination and Purchases of Loans Held-for-sale		176	357	479	593
Principal Balance of Loans Sold, Serviced Loans				2,100			2,000
Loans and Leases Receivable, Gain (Loss) on Sales, Net		4	6	8	9
Principle amount of loans held for sale sold		234	318	550	591
Servicing Asset at Amortized Cost		0	0	$ 0	0
Minimum number of days past due for nonaccrual status | d				90
Recorded investment in TDR loans modified with interest rates below market		129		$ 129		129	128
Additional interest income due to increased cash flows from acquired loans		10	6	13	10
Provision for Loan and Lease Losses		7	35	30	77
Provision for Unfunded Lending Commitments		(3)	4	2	10
Other Real Estate, Foreclosed Assets, and Repossessed Assets		1		1		1	2
Other Real Estate, In Process of Forecloseing Assets		9		9		9	10
Financing Receivable Recorded Investment Thirty To Eighty Nine Days Past Due		124		124		124	150
Financing Receivable Recorded Investments, Equal To and Greater Than 90 Days Past Due		141		141		141	159
Financing Receivable, Recorded Investment, Past Due		265		265		265	309
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing		19		19		19	36
Financing Receivable, Recorded Investment, Nonaccrual Status	[1]	325		325		325	381
Total reversal amount to allowance for loan and lease losses due to an increased cash flows from acquired loans		0		0	0
Commercial [Member]
Loans And Allowance For Credit Losses [Line Items]
Loans and Leases Receivable, Gross		22,203		$ 22,203		22,203	21,615
Subsequent payment default period, number of days | d				90
Provision for Loan and Lease Losses		9	25	$ 32	71
Provision for Unfunded Lending Commitments		(3)	2	0	4
Consumer Portfolio Segment [Member]
Loans And Allowance For Credit Losses [Line Items]
Loans and Leases Receivable, Gross		10,282		$ 10,282		10,282	9,693
Subsequent payment default period, number of days | d				60
Provision for Loan and Lease Losses		3	0	$ 7	(6)
Provision for Unfunded Lending Commitments		0	0	0	1
Financing Receivable, Recorded Investment, Nonaccrual Status		1		1		1	0
Consumer Loan [Member]
Loans And Allowance For Credit Losses [Line Items]
Loans and Leases Receivable, Gross		10,282		10,282		10,282	9,693
Financing Receivable, Recorded Investment, Current		10,225		10,225		10,225	9,638
Financing Receivable Recorded Investment Thirty To Eighty Nine Days Past Due		26		26		26	22
Financing Receivable Recorded Investments, Equal To and Greater Than 90 Days Past Due		31		31		31	33
Financing Receivable, Recorded Investment, Past Due		57		57		57	55
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing		3		3		3	5
Financing Receivable, Recorded Investment, Nonaccrual Status	[1]	21		21		21	17
Consumer Portfolio Segment [Member]
Loans And Allowance For Credit Losses [Line Items]
Loans and Leases Receivable, Gross		188		188		188	190
Financing Receivable, Recorded Investment, Current		187		187		187	189
Financing Receivable Recorded Investment Thirty To Eighty Nine Days Past Due		1		1		1	1
Financing Receivable Recorded Investments, Equal To and Greater Than 90 Days Past Due		0		0		0	0
Financing Receivable, Recorded Investment, Past Due		1		1		1	1
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing		0		0		0	0
Financing Receivable, Recorded Investment, Nonaccrual Status	[1]	0		0		0	0
Finance Leases Portfolio Segment [Member]
Loans And Allowance For Credit Losses [Line Items]
Loans and Leases Receivable, Gross		387		387		387	423
Financing Receivable, Recorded Investment, Current		387		387		387	423
Financing Receivable Recorded Investment Thirty To Eighty Nine Days Past Due		0		0		0	0
Financing Receivable Recorded Investments, Equal To and Greater Than 90 Days Past Due		0		0		0	0
Financing Receivable, Recorded Investment, Past Due		0		0		0	0
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing		0		0		0	0
Financing Receivable, Recorded Investment, Nonaccrual Status	[1]	10		10		10	14
Owner Occupied [Member]
Loans And Allowance For Credit Losses [Line Items]
Loans and Leases Receivable, Gross		7,095		7,095		7,095	6,962
Financing Receivable, Recorded Investment, Current		7,035		7,035		7,035	6,894
Financing Receivable Recorded Investment Thirty To Eighty Nine Days Past Due		26		26		26	40
Financing Receivable Recorded Investments, Equal To and Greater Than 90 Days Past Due		34		34		34	28
Financing Receivable, Recorded Investment, Past Due		60		60		60	68
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing		3		3		3	8
Financing Receivable, Recorded Investment, Nonaccrual Status	[1]	52		52		52	43
Municipal [Member]
Loans And Allowance For Credit Losses [Line Items]
Loans and Leases Receivable, Gross		871		871		871	778
Financing Receivable, Recorded Investment, Current		871		871		871	778
Financing Receivable Recorded Investment Thirty To Eighty Nine Days Past Due		0		0		0	0
Financing Receivable Recorded Investments, Equal To and Greater Than 90 Days Past Due		0		0		0	0
Financing Receivable, Recorded Investment, Past Due		0		0		0	0
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing		0		0		0	0
Financing Receivable, Recorded Investment, Nonaccrual Status	[1]	1		1		1	1
Commercial Loan [Member]
Loans And Allowance For Credit Losses [Line Items]
Loans and Leases Receivable, Gross		22,203		22,203		22,203	21,615
Financing Receivable, Recorded Investment, Current		22,028		22,028		22,028	21,401
Financing Receivable Recorded Investment Thirty To Eighty Nine Days Past Due		80		80		80	112
Financing Receivable Recorded Investments, Equal To and Greater Than 90 Days Past Due		95		95		95	102
Financing Receivable, Recorded Investment, Past Due		175		175		175	214
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing		13		13		13	18
Financing Receivable, Recorded Investment, Nonaccrual Status	[1]	279		279		279	345
Commercial Real Estate Portfolio Segment [Member]
Loans And Allowance For Credit Losses [Line Items]
Loans and Leases Receivable, Gross		2,186		2,186		2,186	2,019
Financing Receivable, Recorded Investment, Current		2,175		2,175		2,175	2,010
Financing Receivable Recorded Investment Thirty To Eighty Nine Days Past Due		6		6		6	7
Financing Receivable Recorded Investments, Equal To and Greater Than 90 Days Past Due		5		5		5	2
Financing Receivable, Recorded Investment, Past Due		11		11		11	9
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing		0		0		0	1
Financing Receivable, Recorded Investment, Nonaccrual Status	[1]	1		1		1	1
Term [Member]
Loans And Allowance For Credit Losses [Line Items]
Loans and Leases Receivable, Gross		9,012		9,012		9,012	9,322
Financing Receivable, Recorded Investment, Current		8,990		8,990		8,990	9,291
Financing Receivable Recorded Investment Thirty To Eighty Nine Days Past Due		12		12		12	9
Financing Receivable Recorded Investments, Equal To and Greater Than 90 Days Past Due		10		10		10	22
Financing Receivable, Recorded Investment, Past Due		22		22		22	31
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing		3		3		3	12
Financing Receivable, Recorded Investment, Nonaccrual Status	[1]	24		24		24	18
Commercial Real Estate [Member]
Loans And Allowance For Credit Losses [Line Items]
Loans and Leases Receivable, Gross		11,198		11,198		11,198	11,341
Financing Receivable, Recorded Investment, Current		11,165		11,165		11,165	11,301
Financing Receivable Recorded Investment Thirty To Eighty Nine Days Past Due		18		18		18	16
Financing Receivable Recorded Investments, Equal To and Greater Than 90 Days Past Due		15		15		15	24
Financing Receivable, Recorded Investment, Past Due		33		33		33	40
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing		3		3		3	13
Financing Receivable, Recorded Investment, Nonaccrual Status	[1]	25		25		25	19
Home Equity Line of Credit [Member]
Loans And Allowance For Credit Losses [Line Items]
Loans and Leases Receivable, Gross		2,697		2,697		2,697	2,645
Financing Receivable, Recorded Investment, Current		2,684		2,684		2,684	2,635
Financing Receivable Recorded Investment Thirty To Eighty Nine Days Past Due		6		6		6	4
Financing Receivable Recorded Investments, Equal To and Greater Than 90 Days Past Due		7		7		7	6
Financing Receivable, Recorded Investment, Past Due		13		13		13	10
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing		2		2		2	1
Financing Receivable, Recorded Investment, Nonaccrual Status	[1]	4		4		4	5
One Through Four Family Residential [Member]
Loans And Allowance For Credit Losses [Line Items]
Loans and Leases Receivable, Gross		6,359		6,359		6,359	5,891
Financing Receivable, Recorded Investment, Current		6,328		6,328		6,328	5,857
Financing Receivable Recorded Investment Thirty To Eighty Nine Days Past Due		10		10		10	12
Financing Receivable Recorded Investments, Equal To and Greater Than 90 Days Past Due		21		21		21	22
Financing Receivable, Recorded Investment, Past Due		31		31		31	34
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing		0		0		0	0
Financing Receivable, Recorded Investment, Nonaccrual Status	[1]	17		17		17	11
Construction And Other Consumer Real Estate [Member]
Loans And Allowance For Credit Losses [Line Items]
Loans and Leases Receivable, Gross		560		560		560	486
Financing Receivable, Recorded Investment, Current		553		553		553	479
Financing Receivable Recorded Investment Thirty To Eighty Nine Days Past Due		6		6		6	3
Financing Receivable Recorded Investments, Equal To and Greater Than 90 Days Past Due		1		1		1	4
Financing Receivable, Recorded Investment, Past Due		7		7		7	7
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing		0		0		0	3
Financing Receivable, Recorded Investment, Nonaccrual Status	[1]	0		0		0	0
Revolving Credit Facility [Member]
Loans And Allowance For Credit Losses [Line Items]
Loans and Leases Receivable, Gross		478		478		478	481
Financing Receivable, Recorded Investment, Current		473		473		473	478
Financing Receivable Recorded Investment Thirty To Eighty Nine Days Past Due		3		3		3	2
Financing Receivable Recorded Investments, Equal To and Greater Than 90 Days Past Due		2		2		2	1
Financing Receivable, Recorded Investment, Past Due		5		5		5	3
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing		1		1		1	1
Financing Receivable, Recorded Investment, Nonaccrual Status	[1]	0		0		0	1
Accruing [Member]
Loans And Allowance For Credit Losses [Line Items]
Financing Receivable, Modifications, Recorded Investment		167		167		167	151
Financing Receivable, Modifications, Subsequent Default, Recorded Investment		0	0	0	0
Nonaccruing [Member]
Loans And Allowance For Credit Losses [Line Items]
Financing Receivable, Modifications, Recorded Investment		304		304		304	251
Financing Receivable, Modifications, Subsequent Default, Recorded Investment		3	$ 19	3	$ 21
Nonaccruing [Member] | Consumer Portfolio Segment [Member]
Loans And Allowance For Credit Losses [Line Items]
Financing Receivable, Modifications, Recorded Investment		$ 11		$ 11		$ 11	$ 12

[1] 1 Represents nonaccrual loans that are not past due more than 30 days; however, full payment of principal and interest is still not expected.