Loans, Leases, and Allowance for Credit Losses (Narrative) (Details)	12 Months Ended
	Dec. 31, 2021 USD ($) mo	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Financing Receivable, Allowance for Credit Losses [Line Items]
Net unamortized purchase premiums, discounts, and deferred loan fees and cost	$ 83,000,000	$ 149,000,000
Accrued interest receivable	161,000,000	200,000,000
Loans and leases, net of unearned income and fees	50,851,000,000	53,476,000,000
Carrying values of loans that have been pledged as collateral	26,800,000,000	24,700,000,000
Held-for-sale loans sold	1,700,000,000	1,800,000,000	$ 900,000,000
Payments for origination and purchases of loans held-for-sale	1,700,000,000	1,800,000,000	900,000,000
Principal balance of loans sold, serviced loans	3,300,000,000	2,700,000,000
Income from loans sold	34,000,000	54,000,000	$ 18,000,000
Financing receivable, commitments threshold for evaluating collectively or individually	1,000,000
Interest income	$ 0	0
Financing receivable, minimum number of months for borrower to meet terms for TDR status | mo	6
Unfunded lending commitments	$ 10,000,000	3,000,000
Recorded investment in TDR loans modified with interest rates below market	326,000,000	311,000,000
Mortgage loans in process of foreclosure	10,000,000	10,000,000
Nonaccruing
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded investment in TDR loans modified with interest rates below market	105,000,000	113,000,000
Financing receivable, modifications, subsequent default, recorded investment	3,000,000	3,000,000
Doubtful
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	0	4,000,000
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	$ 12,198,000,000	12,104,000,000
Financing receivable, period once past due, charged off or charged down (in days)	180 days
Commercial real estate | Nonaccruing
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded investment in TDR loans modified with interest rates below market	$ 16,000,000	20,000,000
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	$ 10,213,000,000	10,900,000,000
Financing receivable, period once past due, charged off or charged down (in days)	180 days
Consumer | Nonaccruing
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded investment in TDR loans modified with interest rates below market	$ 5,000,000	10,000,000
Interest Rate Below Market, Including Multiple Modification Types
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded investment in TDR loans modified with interest rates below market	100,000,000	76,000,000
Land Acquisition and Development | Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	$ 160,000,000	$ 156,000,000
Closed-End Consumer Loans | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, period once past due, charged off or charged down (in days)	120 days