Loans, Leases, and Allowance for Credit Losses (Summary of Nonaccrual Loans) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Financing Receivable, Allowance for Credit Losses [Line Items]
Amortized cost basis with no allowance	$ 96,000,000		$ 96,000,000		$ 139,000,000
Amortized cost basis with allowance	227,000,000		227,000,000		228,000,000
Total amortized cost basis	323,000,000		323,000,000		367,000,000
Related allowance	43,000,000		43,000,000		42,000,000
Interest income	0	$ 0	0	$ 0
Accrued interest receivable written off	4,000,000	6,000,000	12,000,000	15,000,000
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	156,000,000		156,000,000		105,000,000
Total amortized cost basis	224,000,000		224,000,000		216,000,000
Related allowance	33,000,000		33,000,000		26,000,000
Accrued interest receivable written off	3,000,000	5,000,000	11,000,000	13,000,000
Commercial | Commercial and industrial
Financing Receivable, Allowance for Credit Losses [Line Items]
Amortized cost basis with no allowance	27,000,000		27,000,000		73,000,000
Amortized cost basis with allowance	130,000,000		130,000,000		67,000,000
Total amortized cost basis	157,000,000		157,000,000		140,000,000
Related allowance	30,000,000		30,000,000		22,000,000
Commercial | Owner-occupied
Financing Receivable, Allowance for Credit Losses [Line Items]
Amortized cost basis with no allowance	41,000,000		41,000,000		38,000,000
Amortized cost basis with allowance	26,000,000		26,000,000		38,000,000
Total amortized cost basis	67,000,000		67,000,000		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	11,000,000		11,000,000		12,000,000
Amortized cost basis with allowance	14,000,000		14,000,000		19,000,000
Total amortized cost basis	25,000,000		25,000,000		31,000,000
Related allowance	1,000,000		1,000,000		3,000,000
Accrued interest receivable written off	1,000,000	1,000,000	1,000,000	2,000,000
Commercial real estate | Term
Financing Receivable, Allowance for Credit Losses [Line Items]
Amortized cost basis with no allowance	11,000,000		11,000,000		12,000,000
Amortized cost basis with allowance	14,000,000		14,000,000		19,000,000
Total amortized cost basis	25,000,000		25,000,000		31,000,000
Related allowance	1,000,000		1,000,000		3,000,000
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Amortized cost basis with no allowance	17,000,000		17,000,000		16,000,000
Amortized cost basis with allowance	57,000,000		57,000,000		104,000,000
Total amortized cost basis	74,000,000		74,000,000		120,000,000
Related allowance	9,000,000		9,000,000		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	5,000,000		5,000,000		2,000,000
Amortized cost basis with allowance	10,000,000		10,000,000		14,000,000
Total amortized cost basis	15,000,000		15,000,000		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	12,000,000		12,000,000		14,000,000
Amortized cost basis with allowance	46,000,000		46,000,000		89,000,000
Total amortized cost basis	58,000,000		58,000,000		103,000,000
Related allowance	6,000,000		6,000,000		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