Loans (Credit Quality Indicator At Amortized Cost By Origination Year) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	$ 3,340.1		$ 6,875.8
Year two	3,543.0		3,905.4
Year three	3,717.4		3,835.4
Year four	3,619.5		3,176.8
Year five	2,753.2		1,540.2
PRIOR	4,021.9		2,664.7
REVOLVING LOANS	19,097.3		20,656.1
REVOLVING LOANS CONVERTED TO TERM LOANS	740.9		736.2
TOTAL LOANS	40,833.3		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	(0.1)		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	(0.3)	$ (11.1)	(15.5)
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	2,770.8		5,454.6
Year two	2,290.7		2,764.1
Year three	2,635.8		2,261.1
Year four	2,132.9		1,624.2
Year five	1,417.6		428.7
PRIOR	1,057.4		698.9
REVOLVING LOANS	7,068.4		6,948.9
REVOLVING LOANS CONVERTED TO TERM LOANS	108.9		98.3
TOTAL LOANS	19,482.5		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	(0.1)		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	(0.3)	(11.0)	(15.1)
Commercial | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	115.5		1,205.2
Year two	1,291.1		833.9
Year three	776.5		826.2
Year four	763.7		964.7
Year five	805.3		166.8
PRIOR	541.3		423.7
REVOLVING LOANS	6,157.5		6,023.5
REVOLVING LOANS CONVERTED TO TERM LOANS	89.7		93.1
TOTAL LOANS	10,540.6		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	49.7		462.1
Year two	452.8		238.2
Year three	216.9		367.9
Year four	350.8		466.2
Year five	411.4		82.2
PRIOR	365.6		277.2
REVOLVING LOANS	4,716.5		4,364.8
REVOLVING LOANS CONVERTED TO TERM LOANS	26.2		26.5
TOTAL LOANS	6,589.9		6,285.1
Commercial | Commercial and Institutional | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	55.8		708.3
Year two	791.4		506.4
Year three	469.0		392.5
Year four	353.1		428.3
Year five	331.6		82.3
PRIOR	167.4		144.2
REVOLVING LOANS	1,333.4		1,585.1
REVOLVING LOANS CONVERTED TO TERM LOANS	53.6		59.7
TOTAL LOANS	3,555.3		3,906.8
Commercial | Commercial and Institutional | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	10.0		34.8
Year two	46.9		89.3
Year three	90.6		65.8
Year four	59.8		70.2
Year five	62.3		2.3
PRIOR	8.3		2.3
REVOLVING LOANS	107.6		73.6
REVOLVING LOANS CONVERTED TO TERM LOANS	9.9		6.9
TOTAL LOANS	395.4		345.2
Commercial | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	118.6		747.3
Year two	846.9		1,846.3
Year three	1,785.4		1,420.5
Year four	1,355.0		634.5
Year five	612.3		191.3
PRIOR	352.4		218.5
REVOLVING LOANS	229.3		250.6
REVOLVING LOANS CONVERTED TO TERM LOANS	19.2		5.2
TOTAL LOANS	5,319.1		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	(0.1)		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	(0.1)		(2.4)
Commercial | Commercial Real Estate | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	41.8		123.2
Year two	119.3		256.3
Year three	204.2		224.4
Year four	211.1		203.7
Year five	76.9		13.8
PRIOR	61.9		43.7
REVOLVING LOANS	24.0		52.6
REVOLVING LOANS CONVERTED TO TERM LOANS	14.0		0.0
TOTAL LOANS	753.2		917.7
Commercial | Commercial Real Estate | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	76.8		610.1
Year two	726.1		1,574.2
Year three	1,581.2		1,070.4
Year four	972.6		424.8
Year five	529.4		173.2
PRIOR	285.9		174.4
REVOLVING LOANS	205.3		198.0
REVOLVING LOANS CONVERTED TO TERM LOANS	5.2		5.2
TOTAL LOANS	4,382.5		4,230.3
Commercial | Commercial Real Estate | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	0.0		14.0
Year two	1.5		15.8
Year three	0.0		125.7
Year four	171.3		6.0
Year five	6.0		4.3
PRIOR	4.6		0.4
REVOLVING LOANS	0.0		0.0
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0
TOTAL LOANS	183.4		166.2
Commercial | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	1,094.1		1,188.5
Year two	152.7		83.9
Year three	73.9		14.4
Year four	14.2		25.0
Year five	0.0		70.6
PRIOR	163.7		56.7
REVOLVING LOANS	681.6		674.8
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0
TOTAL LOANS	2,180.2		2,113.9
Commercial | Non-U.S. | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	687.8		707.1
Year two	78.8		0.0
Year three	0.0		0.0
Year four	0.0		0.0
Year five	0.0		70.6
PRIOR	110.9		28.8
REVOLVING LOANS	617.4		614.9
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0
TOTAL LOANS	1,494.9		1,421.4
Commercial | Non-U.S. | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	405.8		480.5
Year two	73.9		83.9
Year three	73.9		0.8
Year four	0.8		25.0
Year five	0.0		0.0
PRIOR	52.8		27.9
REVOLVING LOANS	64.2		59.9
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0
TOTAL LOANS	671.4		678.0
Commercial | Non-U.S. | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	0.5		0.9
Year two	0.0		0.0
Year three	0.0		13.6
Year four	13.4		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	13.9		14.5
Commercial | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	1,442.6		2,313.6
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	1,442.6		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	793.3		1,142.4
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	793.3		1,142.4
Commercial | Other | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	649.3		1,171.2
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	649.3		1,171.2
Commercial | Other | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	0.0
Year two	0.0
Year three	0.0
Year four	0.0
Year five	0.0
PRIOR	0.0
REVOLVING LOANS	0.0
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0
TOTAL LOANS	0.0
Personal
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	569.3		1,421.2
Year two	1,252.3		1,141.3
Year three	1,081.6		1,574.3
Year four	1,486.6		1,552.6
Year five	1,335.6		1,111.5
PRIOR	2,964.5		1,965.8
REVOLVING LOANS	12,028.9		13,707.2
REVOLVING LOANS CONVERTED TO TERM LOANS	632.0		637.9
TOTAL LOANS	21,350.8		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	0.0		(0.4)
REVOLVING LOANS, Charge-offs	0.0		0.0
REVOLVING LOANS CONVERTED TO TERM LOANS, Charge-offs	0.0		0.0
Charge-Offs	0.0	$ (0.1)	(0.4)
Personal | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	44.6		500.3
Year two	803.0		710.2
Year three	648.8		468.4
Year four	419.7		428.4
Year five	225.8		131.4
PRIOR	326.0		225.9
REVOLVING LOANS	11,228.5		12,755.6
REVOLVING LOANS CONVERTED TO TERM LOANS	622.8		628.6
TOTAL LOANS	14,319.2		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	0.0
REVOLVING LOANS, Charge-offs	0.0
REVOLVING LOANS CONVERTED TO TERM LOANS, Charge-offs	0.0
Charge-Offs	0.0
Personal | Private Client | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	6.7		251.3
Year two	249.1		33.9
Year three	91.7		84.4
Year four	114.5		37.9
Year five	46.6		7.9
PRIOR	33.8		44.6
REVOLVING LOANS	5,597.6		6,993.2
REVOLVING LOANS CONVERTED TO TERM LOANS	93.8		93.3
TOTAL LOANS	6,233.8		7,546.5
Personal | Private Client | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	37.9		249.0
Year two	553.7		660.2
Year three	541.3		384.0
Year four	305.2		390.5
Year five	179.2		123.5
PRIOR	292.2		181.3
REVOLVING LOANS	5,599.1		5,734.8
REVOLVING LOANS CONVERTED TO TERM LOANS	529.0		535.3
TOTAL LOANS	8,037.6		8,258.6
Personal | Private Client | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	0.0		0.0
Year two	0.2		16.1
Year three	15.8		0.0
Year four	0.0		0.0
Year five	0.0		0.0
PRIOR	0.0		0.0
REVOLVING LOANS	31.8		27.6
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0
TOTAL LOANS	47.8		43.7
Personal | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	131.4		411.9
Year two	419.2		414.1
Year three	416.0		1,090.7
Year four	1,051.9		1,085.1
Year five	1,070.7		980.1
PRIOR	2,602.3		1,714.2
REVOLVING LOANS	419.4		411.7
REVOLVING LOANS CONVERTED TO TERM LOANS	2.1		2.1
TOTAL LOANS	6,113.0		6,109.9
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	101.7		197.5
Year two	179.1		150.5
Year three	147.6		436.7
Year four	372.6		375.2
Year five	364.1		325.7
PRIOR	1,064.7		743.6
REVOLVING LOANS	174.6		114.3
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0
TOTAL LOANS	2,404.4		2,343.5
Personal | Residential Real Estate | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	29.7		212.7
Year two	240.1		263.6
Year three	268.4		647.2
Year four	672.6		706.0
Year five	702.7		652.1
PRIOR	1,504.3		938.1
REVOLVING LOANS	217.5		270.2
REVOLVING LOANS CONVERTED TO TERM LOANS	2.1		2.1
TOTAL LOANS	3,637.4		3,692.0
Personal | Residential Real Estate | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	0.0		1.7
Year two	0.0		0.0
Year three	0.0		6.8
Year four	6.7		3.9
Year five	3.9		2.3
PRIOR	33.3		32.5
REVOLVING LOANS	27.3		27.2
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0
TOTAL LOANS	71.2		74.4
Personal | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	0.0		30.6
Year two	30.1		17.0
Year three	16.8		15.2
Year four	15.0		39.1
Year five	39.1		0.0
PRIOR	36.2		25.7
REVOLVING LOANS	381.0		539.9
REVOLVING LOANS CONVERTED TO TERM LOANS	7.1		7.2
TOTAL LOANS	525.3		674.7
Personal | Non-U.S. | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	0.0		3.3
Year two	3.2		1.0
Year three	0.9		0.0
Year four	0.0		0.0
Year five	0.0		0.0
PRIOR	15.9		6.0
REVOLVING LOANS	131.6		369.6
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0
TOTAL LOANS	151.6		379.9
Personal | Non-U.S. | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	0.0		19.5
Year two	19.1		16.0
Year three	15.9		15.2
Year four	15.0		39.1
Year five	39.1		0.0
PRIOR	8.7		19.6
REVOLVING LOANS	249.4		170.3
REVOLVING LOANS CONVERTED TO TERM LOANS	7.1		7.2
TOTAL LOANS	354.3		286.9
Personal | Non-U.S. | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	0.0		7.8
Year two	7.8		0.0
Year three	0.0		0.0
Year four	0.0		0.0
Year five	0.0		0.0
PRIOR	11.6		0.1
REVOLVING LOANS	0.0		0.0
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0
TOTAL LOANS	19.4		7.9
Personal | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	393.3		478.4
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	393.3		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	294.9		168.5
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	294.9		168.5
Personal | Other | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	98.2		309.9
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	98.2		$ 309.9
Personal | Other | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	0.2
Year two	0.0
Year three	0.0
Year four	0.0
Year five	0.0
PRIOR	0.0
REVOLVING LOANS	0.0
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0
TOTAL LOANS	$ 0.2