Loans (Credit Quality Indicator At Amortized Cost By Origination Year) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Dec. 31, 2025
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	$ 4,891.3		$ 7,843.0
Year two	3,565.7		3,122.0
Year three	2,990.9		2,591.3
Year four	2,351.0		2,759.6
Year five	2,528.9		2,137.0
PRIOR	5,065.9		3,341.4
REVOLVING LOANS	20,435.6		19,439.0
REVOLVING LOANS CONVERTED TO TERM LOANS	676.2		715.0
TOTAL LOANS	42,505.5		41,948.3
Year one, Charge-offs	0.0		(0.2)
Year two, Charge-offs	0.0		0.0
Year three, Charge-offs	0.0		0.0
Year four, Charge-offs	0.0		(2.1)
Year five, Charge-offs	0.0		0.0
Prior, Charge-offs	(0.4)		(1.6)
REVOLVING LOANS, Charge-offs	0.0		0.0
REVOLVING LOANS CONVERTED TO TERM LOANS, Charge-offs	0.0		0.0
Charge-Offs	(0.4)	$ (0.3)	(3.9)
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	4,460.5		6,400.0
Year two	2,306.8		1,999.8
Year three	1,925.9		1,936.6
Year four	1,774.7		1,459.7
Year five	1,257.1		914.3
PRIOR	1,583.6		774.8
REVOLVING LOANS	7,237.7		6,819.3
REVOLVING LOANS CONVERTED TO TERM LOANS	132.5		126.5
TOTAL LOANS	20,678.8		20,431.0
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		(2.1)
Year five, Charge-offs	0.0		0.0
Prior, Charge-offs	(0.4)		(1.4)
REVOLVING LOANS, Charge-offs	0.0		0.0
REVOLVING LOANS CONVERTED TO TERM LOANS, Charge-offs	0.0		0.0
Charge-Offs	(0.4)	(0.3)	(3.5)
Commercial | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	144.2		927.1
Year two	1,045.4		1,106.5
Year three	1,089.9		492.0
Year four	440.0		515.3
Year five	373.6		352.7
PRIOR	476.4		268.8
REVOLVING LOANS	2,889.9		2,829.3
REVOLVING LOANS CONVERTED TO TERM LOANS	109.6		103.6
TOTAL LOANS	6,569.0		6,595.3
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	(0.4)		(1.4)
REVOLVING LOANS, Charge-offs	0.0		0.0
REVOLVING LOANS CONVERTED TO TERM LOANS, Charge-offs	0.0		0.0
Charge-Offs	(0.4)		(1.4)
Commercial | Commercial and Institutional | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	31.9		276.9
Year two	419.8		425.1
Year three	426.6		87.8
Year four	86.9		205.4
Year five	101.2		111.8
PRIOR	208.5		149.5
REVOLVING LOANS	1,227.5		1,205.7
REVOLVING LOANS CONVERTED TO TERM LOANS	57.5		57.6
TOTAL LOANS	2,559.9		2,519.8
Commercial | Commercial and Institutional | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	112.3		561.4
Year two	599.4		661.5
Year three	647.9		353.9
Year four	307.6		263.7
Year five	241.0		219.0
PRIOR	259.4		116.6
REVOLVING LOANS	1,582.2		1,566.1
REVOLVING LOANS CONVERTED TO TERM LOANS	37.6		35.7
TOTAL LOANS	3,787.4		3,777.9
Commercial | Commercial and Institutional | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	0.0		88.8
Year two	26.2		19.9
Year three	15.4		50.3
Year four	45.5		46.2
Year five	31.4		21.9
PRIOR	8.5		2.7
REVOLVING LOANS	80.2		57.5
REVOLVING LOANS CONVERTED TO TERM LOANS	14.5		10.3
TOTAL LOANS	221.7		297.6
Commercial | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	125.7		1,137.1
Year two	1,187.4		755.5
Year three	739.8		1,412.7
Year four	1,310.3		929.5
Year five	861.1		561.6
PRIOR	709.7		219.9
REVOLVING LOANS	200.9		233.0
REVOLVING LOANS CONVERTED TO TERM LOANS	22.9		22.9
TOTAL LOANS	5,157.8		5,272.2
Year one, Charge-offs			0.0
Year two, Charge-offs			0.0
Year three, Charge-offs			0.0
Year four, Charge-offs			(2.1)
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			(2.1)
Commercial | Commercial Real Estate | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	51.5		118.5
Year two	175.5		98.7
Year three	108.2		80.8
Year four	73.1		52.6
Year five	53.5		157.3
PRIOR	160.0		20.8
REVOLVING LOANS	10.3		37.9
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0
TOTAL LOANS	632.1		566.6
Commercial | Commercial Real Estate | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	74.2		946.7
Year two	940.0		654.8
Year three	599.6		1,325.1
Year four	1,222.1		831.4
Year five	769.2		404.3
PRIOR	549.3		198.7
REVOLVING LOANS	190.6		195.1
REVOLVING LOANS CONVERTED TO TERM LOANS	22.9		22.9
TOTAL LOANS	4,367.9		4,579.0
Commercial | Commercial Real Estate | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	0.0		71.9
Year two	71.9		2.0
Year three	32.0		6.8
Year four	15.1		45.5
Year five	38.4		0.0
PRIOR	0.4		0.4
REVOLVING LOANS	0.0		0.0
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0
TOTAL LOANS	157.8		126.6
Commercial | Subscription Finance
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	214.3		281.3
Year two	45.5		68.0
Year three	79.0		31.5
Year four	24.0		0.0
Year five	0.0		0.0
PRIOR	70.3		74.9
REVOLVING LOANS	3,587.0		3,147.7
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0
TOTAL LOANS	4,020.1		3,603.4
Commercial | Subscription Finance | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	212.7		281.3
Year two	45.0		68.0
Year three	79.0		15.4
Year four	11.6		0.0
Year five	0.0		0.0
PRIOR	70.3		74.9
REVOLVING LOANS	3,123.4		2,879.3
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0
TOTAL LOANS	3,542.0		3,318.9
Commercial | Subscription Finance | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	1.6		0.0
Year two	0.5		0.0
Year three	0.0		16.1
Year four	12.4		0.0
Year five	0.0		0.0
PRIOR	0.0		0.0
REVOLVING LOANS	463.6		268.4
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0
TOTAL LOANS	478.1		284.5
Commercial | Fund Finance
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	823.5		726.9
Year two	28.5		0.0
Year three	17.2		0.4
Year four	0.4		14.9
Year five	22.4		0.0
PRIOR	31.9		37.6
REVOLVING LOANS	559.9		577.9
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0
TOTAL LOANS	1,483.8		1,357.7
Commercial | Fund Finance | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	347.4		322.6
Year two	19.9		0.0
Year three	17.2		0.0
Year four	0.4		14.9
Year five	22.4		0.0
PRIOR	31.9		37.6
REVOLVING LOANS	427.6		443.7
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0
TOTAL LOANS	866.8		818.8
Commercial | Fund Finance | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	476.1		404.3
Year two	8.6		0.0
Year three	0.0		0.4
Year four	0.0		0.0
Year five	0.0		0.0
PRIOR	0.0		0.0
REVOLVING LOANS	132.3		134.2
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0
TOTAL LOANS	617.0		538.9
Commercial | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	3,152.8		3,327.6
Year two	0.0		69.8
Year three	0.0		0.0
Year four	0.0		0.0
Year five	0.0		0.0
PRIOR	295.3		173.6
REVOLVING LOANS	0.0		31.4
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0
TOTAL LOANS	3,448.1		3,602.4
Commercial | Other | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	1,764.6		1,886.3
Year two	0.0		51.2
Year three	0.0		0.0
Year four	0.0		0.0
Year five	0.0		0.0
PRIOR	20.0		0.0
REVOLVING LOANS	0.0		24.4
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0
TOTAL LOANS	1,784.6		1,961.9
Commercial | Other | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	1,387.3		1,440.3
Year two	0.0		18.6
Year three	0.0		0.0
Year four	0.0		0.0
Year five	0.0		0.0
PRIOR	275.3		173.6
REVOLVING LOANS	0.0		7.0
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0
TOTAL LOANS	1,662.6		1,639.5
Commercial | Other | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	0.9		1.0
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	0.9		1.0
Personal
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	430.8		1,443.0
Year two	1,258.9		1,122.2
Year three	1,065.0		654.7
Year four	576.3		1,299.9
Year five	1,271.8		1,222.7
PRIOR	3,482.3		2,566.6
REVOLVING LOANS	13,197.9		12,619.7
REVOLVING LOANS CONVERTED TO TERM LOANS	543.7		588.5
TOTAL LOANS	21,826.7		21,517.3
Year one, Charge-offs			(0.2)
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			(0.2)
REVOLVING LOANS, Charge-offs			0.0
REVOLVING LOANS CONVERTED TO TERM LOANS, Charge-offs			0.0
Charge-Offs	0.0	$ 0.0	(0.4)
Personal | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	180.2		601.7
Year two	645.6		719.3
Year three	682.0		289.9
Year four	237.2		372.2
Year five	360.8		198.2
PRIOR	259.8		228.8
REVOLVING LOANS	12,752.1		12,172.6
REVOLVING LOANS CONVERTED TO TERM LOANS	542.0		586.6
TOTAL LOANS	15,659.7		15,169.3
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	32.1		149.9
Year two	166.5		130.7
Year three	166.6		133.0
Year four	102.7		58.7
Year five	59.5		47.2
PRIOR	55.8		44.6
REVOLVING LOANS	6,082.4		5,813.0
REVOLVING LOANS CONVERTED TO TERM LOANS	117.5		38.7
TOTAL LOANS	6,783.1		6,415.8
Personal | Private Client | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	148.1		429.2
Year two	456.8		581.0
Year three	507.9		141.7
Year four	119.4		313.5
Year five	301.3		151.0
PRIOR	204.0		184.2
REVOLVING LOANS	6,653.2		6,350.9
REVOLVING LOANS CONVERTED TO TERM LOANS	424.5		547.9
TOTAL LOANS	8,815.2		8,699.4
Personal | Private Client | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	0.0		22.6
Year two	22.3		7.6
Year three	7.5		15.2
Year four	15.1		0.0
Year five	0.0		0.0
PRIOR	0.0		0.0
REVOLVING LOANS	16.5		8.7
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0
TOTAL LOANS	61.4		54.1
Personal | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	88.1		614.3
Year two	613.3		402.9
Year three	383.0		364.8
Year four	339.1		927.7
Year five	911.0		1,024.5
PRIOR	3,222.5		2,337.8
REVOLVING LOANS	445.8		447.1
REVOLVING LOANS CONVERTED TO TERM LOANS	1.7		1.9
TOTAL LOANS	6,004.5		6,121.0
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 | Residential Real Estate | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	37.9		357.1
Year two	348.9		138.7
Year three	108.6		131.8
Year four	118.6		343.3
Year five	328.9		334.6
PRIOR	1,290.2		993.2
REVOLVING LOANS	235.0		232.3
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0
TOTAL LOANS	2,468.1		2,531.0
Personal | Residential Real Estate | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	50.2		256.2
Year two	263.4		264.2
Year three	274.4		232.1
Year four	219.6		576.3
Year five	573.9		658.6
PRIOR	1,868.2		1,313.0
REVOLVING LOANS	196.6		194.3
REVOLVING LOANS CONVERTED TO TERM LOANS	1.7		1.9
TOTAL LOANS	3,448.0		3,496.6
Personal | Residential Real Estate | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	0.0		1.0
Year two	1.0		0.0
Year three	0.0		0.9
Year four	0.9		8.1
Year five	8.2		31.3
PRIOR	64.1		31.6
REVOLVING LOANS	14.2		20.5
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0
TOTAL LOANS	88.4		93.4
Personal | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	162.5		227.0
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	162.5		227.0
Year one, Charge-offs			(0.2)
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			(0.2)
Personal | Other | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	76.7		86.0
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	76.7		86.0
Personal | Other | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	85.8		141.0
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	$ 85.8		$ 141.0