Loans And Allowance For Credit Losses (Summary Of ALLL And Outstanding Loan Balances According To The Company's Impairment Method) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Financing Receivable, Allowance for Credit Losses [Line Items]
Impaired Financing Receivable, Average Recorded Investment	$ 601	$ 724	$ 559	$ 599
Impaired Financing Receivable, Interest Income, Accrual Method	5	8	23	26
Allowance for loan losses: Individually evaluated for impairment	(33)		(33)			$ (65)
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	508		508			502
Outstanding loan balances: Individually evaluated for impairment	500		500			619
Outstanding loan balances: Collectively evaluated for impairment	43,616		43,616			41,953
Certain Loans and Debt Securities Acquired in Transfer, with Related Allowance for Credit Losses Due to Subsequent Impairment	40		40			77
Loans and Leases Receivable, Gross	44,156		44,156			42,649
Financing Receivable Allowance For Credit Losses and Receivables Acquired With Deteriorated Credit Quality	0		0			0
Loans and Leases Receivable, Allowance	541	597	541	597	$ 544	567	$ 608	$ 606
Owner Occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Impaired Financing Receivable, Average Recorded Investment	104	100	101	103
Impaired Financing Receivable, Interest Income, Accrual Method	2	2	5	8
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Individually evaluated for impairment	(28)		(28)			(56)
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	357		357			364
Outstanding loan balances: Individually evaluated for impairment	352		352			466
Outstanding loan balances: Collectively evaluated for impairment	22,163		22,163			21,111
Certain Loans and Debt Securities Acquired in Transfer, with Related Allowance for Credit Losses Due to Subsequent Impairment	24		24			38
Loans and Leases Receivable, Gross	22,539		22,539			21,615
Financing Receivable Allowance For Credit Losses and Receivables Acquired With Deteriorated Credit Quality	0		0			0
Loans and Leases Receivable, Allowance	385	446	385	446	393	420	457	454
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Impaired Financing Receivable, Average Recorded Investment	10	11	11	12
Impaired Financing Receivable, Interest Income, Accrual Method	0	1	0	2
Loans and Leases Receivable, Allowance	107	121	107	121	116	116	121	114
Consumer Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Impaired Financing Receivable, Average Recorded Investment	1	2	1	2
Impaired Financing Receivable, Interest Income, Accrual Method	0	0	0	0
Allowance for loan losses: Individually evaluated for impairment	(4)		(4)			(6)
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	45		45			25
Outstanding loan balances: Individually evaluated for impairment	70		70			75
Outstanding loan balances: Collectively evaluated for impairment	10,427		10,427			9,611
Certain Loans and Debt Securities Acquired in Transfer, with Related Allowance for Credit Losses Due to Subsequent Impairment	6		6			7
Loans and Leases Receivable, Gross	10,503		10,503			9,693
Financing Receivable Allowance For Credit Losses and Receivables Acquired With Deteriorated Credit Quality	0		0			0
Loans and Leases Receivable, Allowance	49	30	49	30	$ 35	31	$ 30	$ 38
Commercial Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Impaired Financing Receivable, Average Recorded Investment	461	550	413	423
Impaired Financing Receivable, Interest Income, Accrual Method	3	3	10	12
Term [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Impaired Financing Receivable, Average Recorded Investment	53	74	58	79
Impaired Financing Receivable, Interest Income, Accrual Method	1	3	11	9
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Impaired Financing Receivable, Average Recorded Investment	63	85	69	91
Impaired Financing Receivable, Interest Income, Accrual Method	1	4	11	11
Allowance for loan losses: Individually evaluated for impairment	(1)		(1)			(3)
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	106		106			113
Outstanding loan balances: Individually evaluated for impairment	78		78			78
Outstanding loan balances: Collectively evaluated for impairment	11,026		11,026			11,231
Certain Loans and Debt Securities Acquired in Transfer, with Related Allowance for Credit Losses Due to Subsequent Impairment	10		10			32
Loans and Leases Receivable, Gross	11,114		11,114			11,341
Financing Receivable Allowance For Credit Losses and Receivables Acquired With Deteriorated Credit Quality	0		0			0
Loans and Leases Receivable, Allowance	107		107			$ 116
Home Equity Line of Credit [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Impaired Financing Receivable, Average Recorded Investment	21	23	21	22
Impaired Financing Receivable, Interest Income, Accrual Method	0	0	1	1
One Through Four Family Residential [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Impaired Financing Receivable, Average Recorded Investment	53	61	53	58
Impaired Financing Receivable, Interest Income, Accrual Method	1	1	1	2
Construction And Other Consumer Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Impaired Financing Receivable, Average Recorded Investment	2	3	2	3
Impaired Financing Receivable, Interest Income, Accrual Method	0	0	0	0
Consumer Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Impaired Financing Receivable, Average Recorded Investment	77	89	77	85
Impaired Financing Receivable, Interest Income, Accrual Method	1	1	2	3
Municipal [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Impaired Financing Receivable, Average Recorded Investment	1	1	1	1
Impaired Financing Receivable, Interest Income, Accrual Method	$ 0	$ 0	$ 0	$ 0