Loans, Leases, And Allowance For Credit Losses (Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Jun. 30, 2020
Loans And Allowance For Credit Losses [Line Items]
Net unamortized purchase premiums, discounts, and deferred loan fees and cost	$ 191,000,000		$ 191,000,000		$ 60,000,000
Accrued interest receivable	197,000,000		197,000,000		164,000,000
Total loans	54,745,000,000		54,745,000,000		48,709,000,000
Carrying values of loans that have been pledged as collateral	26,300,000,000		26,300,000,000		21,500,000,000
Held-for-sale loans sold	463,000,000	$ 278,000,000	1,400,000,000	$ 527,000,000
Payments for origination and purchases of loans held-for-sale	480,000,000	316,000,000	1,400,000,000	579,000,000
Principal balance of loans sold, serviced loans	2,500,000,000		2,500,000,000		1,700,000,000
Income from loans sold	18,000,000	8,000,000	44,000,000	13,000,000
Financing receivable, commitments threshold for evaluating collectively or individually	1,000,000		1,000,000
Total allowance for credit losses	917,000,000	572,000,000	917,000,000	572,000,000		$ 914,000,000
Unfunded lending commitments on troubled debt restructuring	4,000,000		4,000,000		5,000,000
Recorded investment in TDR loans modified with interest rates below market			281,000,000		153,000,000
Real estate acquired through foreclosure	1,000,000		1,000,000		1,000,000
Mortgage loans in process of foreclosure	7,000,000		7,000,000		8,000,000
Commercial real estate
Loans And Allowance For Credit Losses [Line Items]
Total loans	12,027,000,000		$ 12,027,000,000		11,555,000,000
Financing receivable, period once past due, charged off or charged down			180 days
Total allowance for credit losses	165,000,000	130,000,000	$ 165,000,000	130,000,000
Consumer
Loans And Allowance For Credit Losses [Line Items]
Total loans	11,204,000,000		$ 11,204,000,000		11,766,000,000
Financing receivable, period once past due, charged off or charged down			180 days
Total allowance for credit losses	149,000,000	$ 53,000,000	$ 149,000,000	$ 53,000,000
Interest Rate Below Market, Including Multiple Modification Types
Loans And Allowance For Credit Losses [Line Items]
Recorded investment in TDR loans modified with interest rates below market			62,000,000		73,000,000
Land Acquisition and Development | Commercial real estate
Loans And Allowance For Credit Losses [Line Items]
Total loans	$ 119,000,000		$ 119,000,000		$ 158,000,000
Closed-End Consumer Loans | Consumer
Loans And Allowance For Credit Losses [Line Items]
Financing receivable, period once past due, charged off or charged down			120 days