Loans, Leases, and Allowance for Credit Losses (Summary of Nonaccrual Loans) (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans held for sale, Amortized cost basis with no allowance	$ 1,000,000		$ 1,000,000
Loans held for sale, Amortized cost basis with allowance	0		0
Loans held for sale, Total amortized cost basis	1,000,000		1,000,000
Loans held for sale, Related allowance	0		0
Amortized cost basis with no allowance	100,000,000		100,000,000		$ 139,000,000
Amortized cost basis with allowance	206,000,000		206,000,000		228,000,000
Total amortized cost basis	306,000,000		306,000,000		367,000,000
Related allowance	33,000,000		33,000,000		42,000,000
Interest income	0	$ 0	0	$ 0
Accrued interest receivable written off	5,000,000	5,000,000	8,000,000	9,000,000
Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Amortized cost basis with no allowance	68,000,000		68,000,000		111,000,000
Amortized cost basis with allowance	113,000,000		113,000,000		105,000,000
Total amortized cost basis	181,000,000		181,000,000		216,000,000
Related allowance	23,000,000		23,000,000		26,000,000
Accrued interest receivable written off	4,000,000	4,000,000	7,000,000	8,000,000
Commercial | Commercial and industrial
Financing Receivable, Allowance for Credit Losses [Line Items]
Amortized cost basis with no allowance	32,000,000		32,000,000		73,000,000
Amortized cost basis with allowance	79,000,000		79,000,000		67,000,000
Total amortized cost basis	111,000,000		111,000,000		140,000,000
Related allowance	20,000,000		20,000,000		22,000,000
Commercial | PPP
Financing Receivable, Allowance for Credit Losses [Line Items]
Amortized cost basis with no allowance	0		0
Amortized cost basis with allowance	1,000,000		1,000,000
Total amortized cost basis	1,000,000		1,000,000
Related allowance	0		0
Commercial | Owner-occupied
Financing Receivable, Allowance for Credit Losses [Line Items]
Amortized cost basis with no allowance	36,000,000		36,000,000		38,000,000
Amortized cost basis with allowance	33,000,000		33,000,000		38,000,000
Total amortized cost basis	69,000,000		69,000,000		76,000,000
Related allowance	3,000,000		3,000,000		4,000,000
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Amortized cost basis with no allowance	13,000,000		13,000,000		12,000,000
Amortized cost basis with allowance	15,000,000		15,000,000		19,000,000
Total amortized cost basis	28,000,000		28,000,000		31,000,000
Related allowance	2,000,000		2,000,000		3,000,000
Accrued interest receivable written off	1,000,000	1,000,000	1,000,000	1,000,000
Commercial real estate | Term
Financing Receivable, Allowance for Credit Losses [Line Items]
Amortized cost basis with no allowance	13,000,000		13,000,000		12,000,000
Amortized cost basis with allowance	15,000,000		15,000,000		19,000,000
Total amortized cost basis	28,000,000		28,000,000		31,000,000
Related allowance	2,000,000		2,000,000		3,000,000
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Amortized cost basis with no allowance	19,000,000		19,000,000		16,000,000
Amortized cost basis with allowance	78,000,000		78,000,000		104,000,000
Total amortized cost basis	97,000,000		97,000,000		120,000,000
Related allowance	8,000,000		8,000,000		13,000,000
Accrued interest receivable written off	0	$ 0	0	$ 0
Consumer | Home equity credit line
Financing Receivable, Allowance for Credit Losses [Line Items]
Amortized cost basis with no allowance	6,000,000		6,000,000		2,000,000
Amortized cost basis with allowance	12,000,000		12,000,000		14,000,000
Total amortized cost basis	18,000,000		18,000,000		16,000,000
Related allowance	3,000,000		3,000,000		3,000,000
Consumer | 1-4 family residential
Financing Receivable, Allowance for Credit Losses [Line Items]
Amortized cost basis with no allowance	13,000,000		13,000,000		14,000,000
Amortized cost basis with allowance	65,000,000		65,000,000		89,000,000
Total amortized cost basis	78,000,000		78,000,000		103,000,000
Related allowance	5,000,000		5,000,000		9,000,000
Consumer | Bankcard and other revolving plans
Financing Receivable, Allowance for Credit Losses [Line Items]
Amortized cost basis with no allowance	0		0		0
Amortized cost basis with allowance	1,000,000		1,000,000		1,000,000
Total amortized cost basis	1,000,000		1,000,000		1,000,000
Related allowance	$ 0		$ 0		$ 1,000,000