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
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Allowance for Credit Losses [Line Items]
Impaired Financing Receivable, Average Recorded Investment	$ 655	$ 619
Impaired Financing Receivable, Interest Income, Accrual Method	6	9
Allowance for loan losses: Individually evaluated for impairment	(51)		$ (65)
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	492		502
Outstanding loan balances: Individually evaluated for impairment	645		619
Outstanding loan balances: Collectively evaluated for impairment	42,026		41,953
Certain Loans and Debt Securities Acquired in Transfer, with Related Allowance for Credit Losses Due to Subsequent Impairment	71		77
Loans and Leases Receivable, Gross	42,742		42,649
Financing Receivable Allowance For Credit Losses and Receivables Acquired With Deteriorated Credit Quality	1		0
Loans and Leases Receivable, Allowance	544	612	567	$ 606
Owner Occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Impaired Financing Receivable, Average Recorded Investment	101	122
Impaired Financing Receivable, Interest Income, Accrual Method	2	2
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Individually evaluated for impairment	(43)		(56)
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	354		364
Outstanding loan balances: Individually evaluated for impairment	490		466
Outstanding loan balances: Collectively evaluated for impairment	21,033		21,111
Certain Loans and Debt Securities Acquired in Transfer, with Related Allowance for Credit Losses Due to Subsequent Impairment	33		38
Loans and Leases Receivable, Gross	21,556		21,615
Financing Receivable Allowance For Credit Losses and Receivables Acquired With Deteriorated Credit Quality	0		0
Loans and Leases Receivable, Allowance	397	464	420	454
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Impaired Financing Receivable, Average Recorded Investment	13	15
Impaired Financing Receivable, Interest Income, Accrual Method	0	1
Loans and Leases Receivable, Allowance	114	118	116	114
Consumer Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Impaired Financing Receivable, Average Recorded Investment	1	2
Impaired Financing Receivable, Interest Income, Accrual Method	0	0
Allowance for loan losses: Individually evaluated for impairment	(5)		(6)
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	27		25
Outstanding loan balances: Individually evaluated for impairment	73		75
Outstanding loan balances: Collectively evaluated for impairment	9,900		9,611
Certain Loans and Debt Securities Acquired in Transfer, with Related Allowance for Credit Losses Due to Subsequent Impairment	7		7
Loans and Leases Receivable, Gross	9,980		9,693
Financing Receivable Allowance For Credit Losses and Receivables Acquired With Deteriorated Credit Quality	1		0
Loans and Leases Receivable, Allowance	33	30	31	$ 38
Commercial Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Impaired Financing Receivable, Average Recorded Investment	495	405
Impaired Financing Receivable, Interest Income, Accrual Method	3	4
Term [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Impaired Financing Receivable, Average Recorded Investment	68	106
Impaired Financing Receivable, Interest Income, Accrual Method	2	3
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Impaired Financing Receivable, Average Recorded Investment	81	121
Impaired Financing Receivable, Interest Income, Accrual Method	2	4
Allowance for loan losses: Individually evaluated for impairment	(3)		(3)
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	111		113
Outstanding loan balances: Individually evaluated for impairment	82		78
Outstanding loan balances: Collectively evaluated for impairment	11,093		11,231
Certain Loans and Debt Securities Acquired in Transfer, with Related Allowance for Credit Losses Due to Subsequent Impairment	31		32
Loans and Leases Receivable, Gross	11,206		11,341
Financing Receivable Allowance For Credit Losses and Receivables Acquired With Deteriorated Credit Quality	0		0
Loans and Leases Receivable, Allowance	114		$ 116
Home Equity Line of Credit [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Impaired Financing Receivable, Average Recorded Investment	21	25
Impaired Financing Receivable, Interest Income, Accrual Method	0	0
One Through Four Family Residential [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Impaired Financing Receivable, Average Recorded Investment	54	63
Impaired Financing Receivable, Interest Income, Accrual Method	1	1
Construction And Other Consumer Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Impaired Financing Receivable, Average Recorded Investment	3	3
Impaired Financing Receivable, Interest Income, Accrual Method	0	0
Revolving Credit Facility [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Impaired Financing Receivable, Average Recorded Investment	0	0
Impaired Financing Receivable, Interest Income, Accrual Method	0	0
Consumer Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Impaired Financing Receivable, Average Recorded Investment	79	93
Impaired Financing Receivable, Interest Income, Accrual Method	1	1
Municipal [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Impaired Financing Receivable, Average Recorded Investment	1	1
Impaired Financing Receivable, Interest Income, Accrual Method	$ 0	$ 0