Loans (Credit Quality Indicator At Amortized Cost By Origination Year) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	$ 6,789.0		$ 6,789.0		$ 6,875.8
Year two	3,272.3		3,272.3		3,905.4
Year three	2,954.4		2,954.4		3,835.4
Year four	3,051.1		3,051.1		3,176.8
Year five	2,253.6		2,253.6		1,540.2
PRIOR	3,677.8		3,677.8		2,664.7
REVOLVING LOANS	20,221.9		20,221.9		20,656.1
REVOLVING LOANS CONVERTED TO TERM LOANS	729.3		729.3		736.2
TOTAL LOANS	42,949.4		42,949.4		43,390.6
Year one, Charge-offs			0.0		0.0
Year two, Charge-offs			0.0		(7.3)
Year three, Charge-offs			0.0		(7.8)
Year four, Charge-offs			(2.1)		0.0
Year five, Charge-offs			0.0		0.0
Prior, Charge-offs			(0.4)		(0.4)
REVOLVING LOANS, Charge-offs			0.0		0.0
REVOLVING LOANS CONVERTED TO TERM LOANS, Charge-offs			0.0		0.0
Charge-Offs	(2.1)	$ 0.0	(2.5)	$ (11.4)	(15.5)
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	5,516.3		5,516.3		5,454.6
Year two	2,105.3		2,105.3		2,764.1
Year three	2,234.0		2,234.0		2,261.1
Year four	1,670.3		1,670.3		1,624.2
Year five	997.0		997.0		428.7
PRIOR	1,021.8		1,021.8		698.9
REVOLVING LOANS	6,891.2		6,891.2		6,948.9
REVOLVING LOANS CONVERTED TO TERM LOANS	135.2		135.2		98.3
TOTAL LOANS	20,571.1		20,571.1		20,278.8
Year one, Charge-offs			0.0		0.0
Year two, Charge-offs			0.0		(7.3)
Year three, Charge-offs			0.0		(7.8)
Year four, Charge-offs			(2.1)		0.0
Year five, Charge-offs			0.0		0.0
Prior, Charge-offs			(0.2)		0.0
REVOLVING LOANS, Charge-offs			0.0		0.0
REVOLVING LOANS CONVERTED TO TERM LOANS, Charge-offs			0.0		0.0
Charge-Offs	(2.0)	0.0	(2.3)	(11.0)	(15.1)
Commercial | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	704.4		704.4		1,205.2
Year two	1,140.3		1,140.3		833.9
Year three	636.8		636.8		826.2
Year four	628.4		628.4		964.7
Year five	403.5		403.5		166.8
PRIOR	394.4		394.4		423.7
REVOLVING LOANS	6,216.4		6,216.4		6,023.5
REVOLVING LOANS CONVERTED TO TERM LOANS	119.3		119.3		93.1
TOTAL LOANS	10,243.5		10,243.5		10,537.1
Year one, Charge-offs			0.0		0.0
Year two, Charge-offs			0.0		(7.3)
Year three, Charge-offs			0.0		(5.4)
Year four, Charge-offs			0.0		0.0
Year five, Charge-offs			0.0		0.0
Prior, Charge-offs			(0.2)		0.0
REVOLVING LOANS, Charge-offs			0.0		0.0
REVOLVING LOANS CONVERTED TO TERM LOANS, Charge-offs			0.0		0.0
Charge-Offs			(0.2)		(12.7)
Commercial | Commercial and Institutional | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	216.6		216.6		462.1
Year two	374.1		374.1		238.2
Year three	164.2		164.2		367.9
Year four	285.1		285.1		466.2
Year five	147.1		147.1		82.2
PRIOR	247.9		247.9		277.2
REVOLVING LOANS	4,498.6		4,498.6		4,364.8
REVOLVING LOANS CONVERTED TO TERM LOANS	67.9		67.9		26.5
TOTAL LOANS	6,001.5		6,001.5		6,285.1
Commercial | Commercial and Institutional | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	399.0		399.0		708.3
Year two	745.9		745.9		506.4
Year three	433.1		433.1		392.5
Year four	294.2		294.2		428.3
Year five	241.4		241.4		82.3
PRIOR	138.8		138.8		144.2
REVOLVING LOANS	1,656.8		1,656.8		1,585.1
REVOLVING LOANS CONVERTED TO TERM LOANS	41.0		41.0		59.7
TOTAL LOANS	3,950.2		3,950.2		3,906.8
Commercial | Commercial and Institutional | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	88.8		88.8		34.8
Year two	20.3		20.3		89.3
Year three	39.5		39.5		65.8
Year four	49.1		49.1		70.2
Year five	15.0		15.0		2.3
PRIOR	7.7		7.7		2.3
REVOLVING LOANS	61.0		61.0		73.6
REVOLVING LOANS CONVERTED TO TERM LOANS	10.4		10.4		6.9
TOTAL LOANS	291.8		291.8		345.2
Commercial | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	721.4		721.4		747.3
Year two	824.7		824.7		1,846.3
Year three	1,566.0		1,566.0		1,420.5
Year four	1,028.1		1,028.1		634.5
Year five	593.5		593.5		191.3
PRIOR	261.6		261.6		218.5
REVOLVING LOANS	244.4		244.4		250.6
REVOLVING LOANS CONVERTED TO TERM LOANS	15.9		15.9		5.2
TOTAL LOANS	5,255.6		5,255.6		5,314.2
Year one, Charge-offs			0.0		0.0
Year two, Charge-offs			0.0		0.0
Year three, Charge-offs			0.0		(2.4)
Year four, Charge-offs			(2.1)		0.0
Year five, Charge-offs			0.0		0.0
Prior, Charge-offs			0.0		0.0
REVOLVING LOANS, Charge-offs			0.0		0.0
REVOLVING LOANS CONVERTED TO TERM LOANS, Charge-offs			0.0		0.0
Charge-Offs			(2.1)		(2.4)
Commercial | Commercial Real Estate | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	92.3		92.3		123.2
Year two	135.4		135.4		256.3
Year three	51.6		51.6		224.4
Year four	118.2		118.2		203.7
Year five	139.2		139.2		13.8
PRIOR	26.8		26.8		43.7
REVOLVING LOANS	25.0		25.0		52.6
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0		0.0
TOTAL LOANS	588.5		588.5		917.7
Commercial | Commercial Real Estate | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	560.7		560.7		610.1
Year two	689.3		689.3		1,574.2
Year three	1,507.6		1,507.6		1,070.4
Year four	871.0		871.0		424.8
Year five	448.3		448.3		173.2
PRIOR	230.8		230.8		174.4
REVOLVING LOANS	219.4		219.4		198.0
REVOLVING LOANS CONVERTED TO TERM LOANS	15.9		15.9		5.2
TOTAL LOANS	4,543.0		4,543.0		4,230.3
Commercial | Commercial Real Estate | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	68.4		68.4		14.0
Year two	0.0		0.0		15.8
Year three	6.8		6.8		125.7
Year four	38.9		38.9		6.0
Year five	6.0		6.0		4.3
PRIOR	4.0		4.0		0.4
REVOLVING LOANS	0.0		0.0		0.0
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0		0.0
TOTAL LOANS	124.1		124.1		166.2
Commercial | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	1,808.0		1,808.0		1,188.5
Year two	140.3		140.3		83.9
Year three	31.2		31.2		14.4
Year four	13.8		13.8		25.0
Year five	0.0		0.0		70.6
PRIOR	365.8		365.8		56.7
REVOLVING LOANS	430.4		430.4		674.8
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0		0.0
TOTAL LOANS	2,789.5		2,789.5		2,113.9
Commercial | Non-U.S. | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	968.5		968.5		707.1
Year two	131.7		131.7		0.0
Year three	31.2		31.2		0.0
Year four	0.0		0.0		0.0
Year five	0.0		0.0		70.6
PRIOR	168.7		168.7		28.8
REVOLVING LOANS	295.5		295.5		614.9
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0		0.0
TOTAL LOANS	1,595.6		1,595.6		1,421.4
Commercial | Non-U.S. | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	839.0		839.0		480.5
Year two	8.6		8.6		83.9
Year three	0.0		0.0		0.8
Year four	0.8		0.8		25.0
Year five	0.0		0.0		0.0
PRIOR	197.1		197.1		27.9
REVOLVING LOANS	116.8		116.8		59.9
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0		0.0
TOTAL LOANS	1,162.3		1,162.3		678.0
Commercial | Non-U.S. | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	0.5		0.5		0.9
Year two	0.0		0.0		0.0
Year three	0.0		0.0		13.6
Year four	13.0		13.0		0.0
Year five	0.0		0.0		0.0
PRIOR	0.0		0.0		0.0
REVOLVING LOANS	18.1		18.1		0.0
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0		0.0
TOTAL LOANS	31.6		31.6		14.5
Commercial | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	2,282.5		2,282.5		2,313.6
Year two	0.0		0.0		0.0
Year three	0.0		0.0		0.0
Year four	0.0		0.0		0.0
Year five	0.0		0.0		0.0
PRIOR	0.0		0.0		0.0
REVOLVING LOANS	0.0		0.0		0.0
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0		0.0
TOTAL LOANS	2,282.5		2,282.5		2,313.6
Year one, Charge-offs					0.0
Year two, Charge-offs					0.0
Year three, Charge-offs					0.0
Year four, Charge-offs					0.0
Year five, Charge-offs					0.0
Prior, Charge-offs					0.0
REVOLVING LOANS, Charge-offs					0.0
REVOLVING LOANS CONVERTED TO TERM LOANS, Charge-offs					0.0
Charge-Offs					0.0
Commercial | Other | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	1,356.3		1,356.3		1,142.4
Year two	0.0		0.0		0.0
Year three	0.0		0.0		0.0
Year four	0.0		0.0		0.0
Year five	0.0		0.0		0.0
PRIOR	0.0		0.0		0.0
REVOLVING LOANS	0.0		0.0		0.0
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0		0.0
TOTAL LOANS	1,356.3		1,356.3		1,142.4
Commercial | Other | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	925.8		925.8		1,171.2
Year two	0.0		0.0		0.0
Year three	0.0		0.0		0.0
Year four	0.0		0.0		0.0
Year five	0.0		0.0		0.0
PRIOR	0.0		0.0		0.0
REVOLVING LOANS	0.0		0.0		0.0
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0		0.0
TOTAL LOANS	925.8		925.8		1,171.2
Commercial | Other | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	0.4		0.4
Year two	0.0		0.0
Year three	0.0		0.0
Year four	0.0		0.0
Year five	0.0		0.0
PRIOR	0.0		0.0
REVOLVING LOANS	0.0		0.0
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0
TOTAL LOANS	0.4		0.4
Personal
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	1,272.7		1,272.7		1,421.2
Year two	1,167.0		1,167.0		1,141.3
Year three	720.4		720.4		1,574.3
Year four	1,380.8		1,380.8		1,552.6
Year five	1,256.6		1,256.6		1,111.5
PRIOR	2,656.0		2,656.0		1,965.8
REVOLVING LOANS	13,330.7		13,330.7		13,707.2
REVOLVING LOANS CONVERTED TO TERM LOANS	594.1		594.1		637.9
TOTAL LOANS	22,378.3		22,378.3		23,111.8
Year one, Charge-offs			0.0		0.0
Year two, Charge-offs			0.0		0.0
Year three, Charge-offs			0.0		0.0
Year four, Charge-offs			0.0		0.0
Year five, Charge-offs			0.0		0.0
Prior, Charge-offs			(0.2)		(0.4)
REVOLVING LOANS, Charge-offs			0.0		0.0
REVOLVING LOANS CONVERTED TO TERM LOANS, Charge-offs			0.0		0.0
Charge-Offs	(0.1)	$ 0.0	(0.2)	$ (0.4)	(0.4)
Personal | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	282.4		282.4		500.3
Year two	732.0		732.0		710.2
Year three	318.2		318.2		468.4
Year four	386.1		386.1		428.4
Year five	206.6		206.6		131.4
PRIOR	219.0		219.0		225.9
REVOLVING LOANS	12,567.6		12,567.6		12,755.6
REVOLVING LOANS CONVERTED TO TERM LOANS	579.0		579.0		628.6
TOTAL LOANS	15,290.9		15,290.9		15,848.8
Year one, Charge-offs			0.0
Year two, Charge-offs			0.0
Year three, Charge-offs			0.0
Year four, Charge-offs			0.0
Year five, Charge-offs			0.0
Prior, Charge-offs			(0.1)
REVOLVING LOANS, Charge-offs			0.0
REVOLVING LOANS CONVERTED TO TERM LOANS, Charge-offs			0.0
Charge-Offs			(0.1)
Personal | Private Client | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	126.2		126.2		251.3
Year two	96.1		96.1		33.9
Year three	109.9		109.9		84.4
Year four	113.1		113.1		37.9
Year five	49.9		49.9		7.9
PRIOR	25.2		25.2		44.6
REVOLVING LOANS	6,777.5		6,777.5		6,993.2
REVOLVING LOANS CONVERTED TO TERM LOANS	137.9		137.9		93.3
TOTAL LOANS	7,435.8		7,435.8		7,546.5
Personal | Private Client | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	156.2		156.2		249.0
Year two	635.9		635.9		660.2
Year three	192.9		192.9		384.0
Year four	273.0		273.0		390.5
Year five	156.7		156.7		123.5
PRIOR	193.8		193.8		181.3
REVOLVING LOANS	5,782.9		5,782.9		5,734.8
REVOLVING LOANS CONVERTED TO TERM LOANS	441.1		441.1		535.3
TOTAL LOANS	7,832.5		7,832.5		8,258.6
Personal | Private Client | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	0.0		0.0		0.0
Year two	0.0		0.0		16.1
Year three	15.4		15.4		0.0
Year four	0.0		0.0		0.0
Year five	0.0		0.0		0.0
PRIOR	0.0		0.0		0.0
REVOLVING LOANS	7.2		7.2		27.6
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0		0.0
TOTAL LOANS	22.6		22.6		43.7
Personal | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	424.3		424.3		411.9
Year two	412.8		412.8		414.1
Year three	389.4		389.4		1,090.7
Year four	979.8		979.8		1,085.1
Year five	1,026.6		1,026.6		980.1
PRIOR	2,414.4		2,414.4		1,714.2
REVOLVING LOANS	390.7		390.7		411.7
REVOLVING LOANS CONVERTED TO TERM LOANS	7.6		7.6		2.1
TOTAL LOANS	6,045.6		6,045.6		6,109.9
Year one, Charge-offs			0.0		0.0
Year two, Charge-offs			0.0		0.0
Year three, Charge-offs			0.0		0.0
Year four, Charge-offs			0.0		0.0
Year five, Charge-offs			0.0		0.0
Prior, Charge-offs			(0.1)		(0.1)
REVOLVING LOANS, Charge-offs			0.0		0.0
REVOLVING LOANS CONVERTED TO TERM LOANS, Charge-offs			0.0		0.0
Charge-Offs			(0.1)		(0.1)
Personal | Residential Real Estate | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	243.6		243.6		197.5
Year two	164.3		164.3		150.5
Year three	140.3		140.3		436.7
Year four	394.1		394.1		375.2
Year five	385.8		385.8		325.7
PRIOR	993.6		993.6		743.6
REVOLVING LOANS	190.0		190.0		114.3
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0		0.0
TOTAL LOANS	2,511.7		2,511.7		2,343.5
Personal | Residential Real Estate | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	180.7		180.7		212.7
Year two	248.5		248.5		263.6
Year three	249.1		249.1		647.2
Year four	579.1		579.1		706.0
Year five	632.5		632.5		652.1
PRIOR	1,389.3		1,389.3		938.1
REVOLVING LOANS	184.9		184.9		270.2
REVOLVING LOANS CONVERTED TO TERM LOANS	1.9		1.9		2.1
TOTAL LOANS	3,466.0		3,466.0		3,692.0
Personal | Residential Real Estate | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	0.0		0.0		1.7
Year two	0.0		0.0		0.0
Year three	0.0		0.0		6.8
Year four	6.6		6.6		3.9
Year five	8.3		8.3		2.3
PRIOR	31.5		31.5		32.5
REVOLVING LOANS	15.8		15.8		27.2
REVOLVING LOANS CONVERTED TO TERM LOANS	5.7		5.7		0.0
TOTAL LOANS	67.9		67.9		74.4
Personal | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	26.5		26.5		30.6
Year two	22.2		22.2		17.0
Year three	12.8		12.8		15.2
Year four	14.9		14.9		39.1
Year five	23.4		23.4		0.0
PRIOR	22.6		22.6		25.7
REVOLVING LOANS	372.4		372.4		539.9
REVOLVING LOANS CONVERTED TO TERM LOANS	7.5		7.5		7.2
TOTAL LOANS	502.3		502.3		674.7
Personal | Non-U.S. | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	2.6		2.6		3.3
Year two	0.0		0.0		1.0
Year three	0.0		0.0		0.0
Year four	0.0		0.0		0.0
Year five	0.6		0.6		0.0
PRIOR	11.6		11.6		6.0
REVOLVING LOANS	109.2		109.2		369.6
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0		0.0
TOTAL LOANS	124.0		124.0		379.9
Personal | Non-U.S. | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	23.9		23.9		19.5
Year two	14.6		14.6		16.0
Year three	12.8		12.8		15.2
Year four	8.9		8.9		39.1
Year five	22.8		22.8		0.0
PRIOR	10.9		10.9		19.6
REVOLVING LOANS	263.2		263.2		170.3
REVOLVING LOANS CONVERTED TO TERM LOANS	7.5		7.5		7.2
TOTAL LOANS	364.6		364.6		286.9
Personal | Non-U.S. | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	0.0		0.0		7.8
Year two	7.6		7.6		0.0
Year three	0.0		0.0		0.0
Year four	6.0		6.0		0.0
Year five	0.0		0.0		0.0
PRIOR	0.1		0.1		0.1
REVOLVING LOANS	0.0		0.0		0.0
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0		0.0
TOTAL LOANS	13.7		13.7		7.9
Personal | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	539.5		539.5		478.4
Year two	0.0		0.0		0.0
Year three	0.0		0.0		0.0
Year four	0.0		0.0		0.0
Year five	0.0		0.0		0.0
PRIOR	0.0		0.0		0.0
REVOLVING LOANS	0.0		0.0		0.0
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0		0.0
TOTAL LOANS	539.5		539.5		478.4
Year one, Charge-offs					0.0
Year two, Charge-offs					0.0
Year three, Charge-offs					0.0
Year four, Charge-offs					0.0
Year five, Charge-offs					0.0
Prior, Charge-offs					(0.3)
REVOLVING LOANS, Charge-offs					0.0
REVOLVING LOANS CONVERTED TO TERM LOANS, Charge-offs					0.0
Charge-Offs					(0.3)
Personal | Other | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	281.8		281.8		168.5
Year two	0.0		0.0		0.0
Year three	0.0		0.0		0.0
Year four	0.0		0.0		0.0
Year five	0.0		0.0		0.0
PRIOR	0.0		0.0		0.0
REVOLVING LOANS	0.0		0.0		0.0
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0		0.0
TOTAL LOANS	281.8		281.8		168.5
Personal | Other | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	257.7		257.7		309.9
Year two	0.0		0.0		0.0
Year three	0.0		0.0		0.0
Year four	0.0		0.0		0.0
Year five	0.0		0.0		0.0
PRIOR	0.0		0.0		0.0
REVOLVING LOANS	0.0		0.0		0.0
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0		0.0
TOTAL LOANS	257.7		257.7		$ 309.9
Personal | Other | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	0.0		0.0
Year two	0.0		0.0
Year three	0.0		0.0
Year four	0.0		0.0
Year five	0.0		0.0
PRIOR	0.0		0.0
REVOLVING LOANS	0.0		0.0
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0
TOTAL LOANS	$ 0.0		$ 0.0