Loans (Credit Quality Indicator At Amortized Cost By Origination Year) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	$ 5,000.0		$ 5,000.0		$ 13,006.4
2023/2022	4,428.1		4,428.1		4,823.9
2022/2021	4,334.1		4,334.1		4,177.6
2021/2020	3,697.9		3,697.9		1,765.4
2020/2019	1,555.7		1,555.7		1,208.7
PRIOR	3,205.1		3,205.1		2,681.5
REVOLVING LOANS	19,188.0		19,188.0		19,233.5
REVOLVING LOANS CONVERTED TO TERM LOANS	726.3		726.3		720.0
TOTAL LOANS	42,135.2		42,135.2		47,617.0
2024/2023, Charge-offs			0.0		(2.1)
2023/2022, Charge-offs			(7.3)		(4.4)
2022/2021, Charge-offs			(3.7)		0.0
2021/2020, Charge-offs			0.0		0.0
2020/2019, Charge-offs			0.0		0.0
Prior, Charge-offs			(0.4)		(1.0)
REVOLVING LOANS, Charge-offs			0.0		0.0
REVOLVING LOANS CONVERTED TO TERM LOANS, Charge-offs			0.0		0.0
Charge-Offs	(0.3)	$ (0.8)	(11.4)	$ (4.8)	(7.5)
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	4,342.7		4,342.7		10,601.2
2023/2022	3,186.6		3,186.6		3,008.8
2022/2021	2,683.8		2,683.8		2,212.4
2021/2020	1,987.9		1,987.9		536.3
2020/2019	390.6		390.6		590.8
PRIOR	1,067.5		1,067.5		899.0
REVOLVING LOANS	7,080.1		7,080.1		7,467.6
REVOLVING LOANS CONVERTED TO TERM LOANS	94.8		94.8		96.7
TOTAL LOANS	20,834.0		20,834.0		25,412.8
2024/2023, Charge-offs			0.0		(1.3)
2023/2022, Charge-offs			(7.3)		(4.4)
2022/2021, Charge-offs			(3.7)		0.0
2021/2020, Charge-offs			0.0		0.0
2020/2019, 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	0.0	0.0	(11.0)	(4.0)	(5.7)
Commercial | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	530.4		530.4		1,259.1
2023/2022	1,105.5		1,105.5		1,395.0
2022/2021	1,162.1		1,162.1		1,458.6
2021/2020	1,284.3		1,284.3		228.8
2020/2019	177.4		177.4		257.8
PRIOR	563.5		563.5		590.3
REVOLVING LOANS	5,899.4		5,899.4		6,276.9
REVOLVING LOANS CONVERTED TO TERM LOANS	89.5		89.5		88.8
TOTAL LOANS	10,812.1		10,812.1		11,555.3
2024/2023, Charge-offs			0.0
2023/2022, Charge-offs			(7.3)
2022/2021, Charge-offs			(1.3)
2021/2020, Charge-offs			0.0
2020/2019, 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			(8.6)
Commercial | Commercial and Institutional | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	336.4		336.4		443.9
2023/2022	392.7		392.7		534.1
2022/2021	434.9		434.9		668.3
2021/2020	639.8		639.8		78.1
2020/2019	66.7		66.7		137.2
PRIOR	390.9		390.9		409.9
REVOLVING LOANS	4,313.7		4,313.7		4,909.8
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0		15.0
TOTAL LOANS	6,575.1		6,575.1		7,196.3
Commercial | Commercial and Institutional | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	181.3		181.3		801.4
2023/2022	645.8		645.8		790.9
2022/2021	618.1		618.1		729.5
2021/2020	545.9		545.9		138.7
2020/2019	110.7		110.7		120.5
PRIOR	170.9		170.9		178.7
REVOLVING LOANS	1,545.5		1,545.5		1,332.4
REVOLVING LOANS CONVERTED TO TERM LOANS	87.7		87.7		72.0
TOTAL LOANS	3,905.9		3,905.9		4,164.1
Commercial | Commercial and Institutional | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	12.7		12.7		13.8
2023/2022	67.0		67.0		70.0
2022/2021	109.1		109.1		60.8
2021/2020	98.6		98.6		12.0
2020/2019	0.0		0.0		0.1
PRIOR	1.7		1.7		1.7
REVOLVING LOANS	40.2		40.2		34.7
REVOLVING LOANS CONVERTED TO TERM LOANS	1.8		1.8		1.8
TOTAL LOANS	331.1		331.1		194.9
Commercial | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	259.3		259.3		1,933.2
2023/2022	2,019.9		2,019.9		1,598.7
2022/2021	1,506.9		1,506.9		710.6
2021/2020	672.6		672.6		242.3
2020/2019	213.2		213.2		298.8
PRIOR	343.7		343.7		155.4
REVOLVING LOANS	245.9		245.9		187.3
REVOLVING LOANS CONVERTED TO TERM LOANS	5.3		5.3		7.9
TOTAL LOANS	5,266.8		5,266.8		5,134.2
2024/2023, Charge-offs			0.0		(0.7)
2023/2022, Charge-offs			0.0		(4.4)
2022/2021, Charge-offs			(2.4)		0.0
2021/2020, Charge-offs			0.0		0.0
2020/2019, 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			(2.4)		(5.1)
Commercial | Commercial Real Estate | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	48.7		48.7		403.6
2023/2022	453.4		453.4		389.9
2022/2021	318.3		318.3		159.1
2021/2020	195.1		195.1		23.9
2020/2019	25.7		25.7		37.8
PRIOR	37.2		37.2		44.8
REVOLVING LOANS	68.8		68.8		51.0
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0		0.0
TOTAL LOANS	1,147.2		1,147.2		1,110.1
Commercial | Commercial Real Estate | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	197.9		197.9		1,513.5
2023/2022	1,550.5		1,550.5		1,208.8
2022/2021	1,153.5		1,153.5		521.0
2021/2020	460.3		460.3		218.4
2020/2019	183.1		183.1		252.8
PRIOR	300.3		300.3		96.0
REVOLVING LOANS	177.1		177.1		136.3
REVOLVING LOANS CONVERTED TO TERM LOANS	5.3		5.3		7.9
TOTAL LOANS	4,028.0		4,028.0		3,954.7
Commercial | Commercial Real Estate | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	12.7		12.7		16.1
2023/2022	16.0		16.0		0.0
2022/2021	35.1		35.1		30.5
2021/2020	17.2		17.2		0.0
2020/2019	4.4		4.4		8.2
PRIOR	6.2		6.2		14.6
REVOLVING LOANS	0.0		0.0		0.0
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0		0.0
TOTAL LOANS	91.6		91.6		69.4
Commercial | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	1,261.9		1,261.9		1,464.1
2023/2022	61.2		61.2		15.1
2022/2021	14.8		14.8		43.2
2021/2020	31.0		31.0		65.2
2020/2019	0.0		0.0		34.2
PRIOR	160.3		160.3		153.3
REVOLVING LOANS	934.8		934.8		1,003.4
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0		0.0
TOTAL LOANS	2,464.0		2,464.0		2,778.5
Commercial | Non-U.S. | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	770.7		770.7		487.9
2023/2022	0.0		0.0		0.0
2022/2021	0.0		0.0		43.2
2021/2020	31.0		31.0		65.2
2020/2019	0.0		0.0		34.2
PRIOR	30.3		30.3		3.3
REVOLVING LOANS	783.1		783.1		760.0
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0		0.0
TOTAL LOANS	1,615.1		1,615.1		1,393.8
Commercial | Non-U.S. | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	490.6		490.6		974.7
2023/2022	61.2		61.2		0.8
2022/2021	0.8		0.8		0.0
2021/2020	0.0		0.0		0.0
2020/2019	0.0		0.0		0.0
PRIOR	130.0		130.0		150.0
REVOLVING LOANS	151.7		151.7		243.4
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0		0.0
TOTAL LOANS	834.3		834.3		1,368.9
Commercial | Non-U.S. | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	0.6		0.6		1.5
2023/2022	0.0		0.0		14.3
2022/2021	14.0		14.0		0.0
2021/2020	0.0		0.0		0.0
2020/2019	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	14.6		14.6		15.8
Commercial | Other
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	2,291.1		2,291.1		5,944.8
2023/2022	0.0		0.0		0.0
2022/2021	0.0		0.0		0.0
2021/2020	0.0		0.0		0.0
2020/2019	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	2,291.1		2,291.1		5,944.8
2024/2023, Charge-offs	0.0				(0.6)
2023/2022, Charge-offs	0.0				0.0
2022/2021, Charge-offs	0.0				0.0
2021/2020, Charge-offs	0.0				0.0
2020/2019, 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	0.0				(0.6)
Commercial | Other | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	1,052.1		1,052.1		4,313.2
2023/2022	0.0		0.0		0.0
2022/2021	0.0		0.0		0.0
2021/2020	0.0		0.0		0.0
2020/2019	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	1,052.1		1,052.1		4,313.2
Commercial | Other | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	1,239.0		1,239.0		1,631.6
2023/2022	0.0		0.0		0.0
2022/2021	0.0		0.0		0.0
2021/2020	0.0		0.0		0.0
2020/2019	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	1,239.0		1,239.0		1,631.6
Personal
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	657.3		657.3		2,405.2
2023/2022	1,241.5		1,241.5		1,815.1
2022/2021	1,650.3		1,650.3		1,965.2
2021/2020	1,710.0		1,710.0		1,229.1
2020/2019	1,165.1		1,165.1		617.9
PRIOR	2,137.6		2,137.6		1,782.5
REVOLVING LOANS	12,107.9		12,107.9		11,765.9
REVOLVING LOANS CONVERTED TO TERM LOANS	631.5		631.5		623.3
TOTAL LOANS	21,301.2		21,301.2		22,204.2
2024/2023, Charge-offs			0.0		(0.8)
2023/2022, Charge-offs			0.0		0.0
2022/2021, Charge-offs			0.0		0.0
2021/2020, Charge-offs			0.0		0.0
2020/2019, Charge-offs			0.0		0.0
Prior, Charge-offs			(0.4)		(1.0)
REVOLVING LOANS, Charge-offs			0.0		0.0
REVOLVING LOANS CONVERTED TO TERM LOANS, Charge-offs			0.0		0.0
Charge-Offs	(0.3)	$ (0.8)	(0.4)	$ (0.8)	(1.8)
Personal | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	200.3		200.3		818.4
2023/2022	765.3		765.3		629.3
2022/2021	495.8		495.8		707.4
2021/2020	533.8		533.8		168.4
2020/2019	142.4		142.4		167.5
PRIOR	238.0		238.0		197.7
REVOLVING LOANS	11,418.9		11,418.9		11,055.4
REVOLVING LOANS CONVERTED TO TERM LOANS	622.0		622.0		615.9
TOTAL LOANS	14,416.5		14,416.5		14,360.0
2024/2023, Charge-offs			0.0
2023/2022, Charge-offs			0.0
2022/2021, Charge-offs			0.0
2021/2020, Charge-offs			0.0
2020/2019, 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 | Private Client | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	130.8		130.8		504.7
2023/2022	418.8		418.8		140.8
2022/2021	95.6		95.6		52.3
2021/2020	19.6		19.6		67.5
2020/2019	13.9		13.9		8.7
PRIOR	57.3		57.3		134.7
REVOLVING LOANS	5,169.4		5,169.4		5,320.9
REVOLVING LOANS CONVERTED TO TERM LOANS	167.6		167.6		168.1
TOTAL LOANS	6,073.0		6,073.0		6,397.7
Personal | Private Client | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	69.5		69.5		290.1
2023/2022	330.1		330.1		488.2
2022/2021	400.2		400.2		655.1
2021/2020	514.2		514.2		100.9
2020/2019	128.5		128.5		158.8
PRIOR	180.7		180.7		44.7
REVOLVING LOANS	6,238.0		6,238.0		5,721.5
REVOLVING LOANS CONVERTED TO TERM LOANS	454.4		454.4		447.8
TOTAL LOANS	8,315.6		8,315.6		7,907.1
Personal | Private Client | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	0.0		0.0		23.6
2023/2022	16.4		16.4		0.3
2022/2021	0.0		0.0		0.0
2021/2020	0.0		0.0		0.0
2020/2019	0.0		0.0		0.0
PRIOR	0.0		0.0		18.3
REVOLVING LOANS	11.5		11.5		13.0
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0		0.0
TOTAL LOANS	27.9		27.9		55.2
Personal | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	192.8		192.8		470.3
2023/2022	456.8		456.8		1,169.8
2022/2021	1,139.0		1,139.0		1,218.0
2021/2020	1,137.0		1,137.0		1,060.7
2020/2019	1,022.7		1,022.7		434.0
PRIOR	1,872.3		1,872.3		1,571.3
REVOLVING LOANS	386.3		386.3		403.0
REVOLVING LOANS CONVERTED TO TERM LOANS	2.1		2.1		0.0
TOTAL LOANS	6,209.0		6,209.0		6,327.1
2024/2023, Charge-offs			0.0		(0.8)
2023/2022, Charge-offs			0.0		0.0
2022/2021, Charge-offs			0.0		0.0
2021/2020, Charge-offs			0.0		0.0
2020/2019, Charge-offs			0.0		0.0
Prior, Charge-offs			(0.1)		(1.0)
REVOLVING LOANS, Charge-offs			0.0		0.0
REVOLVING LOANS CONVERTED TO TERM LOANS, Charge-offs			0.0		0.0
Charge-Offs			(0.1)		(1.8)
Personal | Residential Real Estate | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	103.5		103.5		278.7
2023/2022	244.7		244.7		464.0
2022/2021	463.2		463.2		500.6
2021/2020	413.6		413.6		373.3
2020/2019	286.6		286.6		142.4
PRIOR	854.3		854.3		722.4
REVOLVING LOANS	191.4		191.4		219.8
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0		0.0
TOTAL LOANS	2,557.3		2,557.3		2,701.2
Personal | Residential Real Estate | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	89.3		89.3		191.6
2023/2022	212.1		212.1		694.9
2022/2021	668.5		668.5		717.4
2021/2020	723.4		723.4		686.7
2020/2019	735.5		735.5		290.0
PRIOR	975.4		975.4		805.3
REVOLVING LOANS	179.0		179.0		170.3
REVOLVING LOANS CONVERTED TO TERM LOANS	2.1		2.1		0.0
TOTAL LOANS	3,585.3		3,585.3		3,556.2
Personal | Residential Real Estate | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	0.0		0.0		0.0
2023/2022	0.0		0.0		10.9
2022/2021	7.3		7.3		0.0
2021/2020	0.0		0.0		0.7
2020/2019	0.6		0.6		1.6
PRIOR	42.6		42.6		43.6
REVOLVING LOANS	15.9		15.9		12.9
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0		0.0
TOTAL LOANS	66.4		66.4		69.7
Personal | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	26.3		26.3		28.2
2023/2022	19.4		19.4		16.0
2022/2021	15.5		15.5		39.8
2021/2020	39.2		39.2		0.0
2020/2019	0.0		0.0		16.4
PRIOR	27.3		27.3		13.5
REVOLVING LOANS	302.7		302.7		307.5
REVOLVING LOANS CONVERTED TO TERM LOANS	7.4		7.4		7.4
TOTAL LOANS	437.8		437.8		428.8
Personal | Non-U.S. | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	1.3		1.3		15.5
2023/2022	1.2		1.2		0.0
2022/2021	0.0		0.0		0.6
2021/2020	0.0		0.0		0.0
2020/2019	0.0		0.0		0.0
PRIOR	6.2		6.2		4.6
REVOLVING LOANS	101.2		101.2		71.4
REVOLVING LOANS CONVERTED TO TERM LOANS	0.0		0.0		0.0
TOTAL LOANS	109.9		109.9		92.1
Personal | Non-U.S. | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	17.1		17.1		12.7
2023/2022	18.2		18.2		16.0
2022/2021	15.5		15.5		39.2
2021/2020	39.2		39.2		0.0
2020/2019	0.0		0.0		16.4
PRIOR	21.1		21.1		8.9
REVOLVING LOANS	201.5		201.5		236.1
REVOLVING LOANS CONVERTED TO TERM LOANS	7.4		7.4		7.4
TOTAL LOANS	320.0		320.0		336.7
Personal | Non-U.S. | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	7.9		7.9		0.0
2023/2022	0.0		0.0		0.0
2022/2021	0.0		0.0		0.0
2021/2020	0.0		0.0		0.0
2020/2019	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	7.9		7.9		0.0
Personal | Other
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	237.9		237.9		1,088.3
2023/2022	0.0		0.0		0.0
2022/2021	0.0		0.0		0.0
2021/2020	0.0		0.0		0.0
2020/2019	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	237.9		237.9		1,088.3
Personal | Other | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	168.8		168.8		461.7
2023/2022	0.0		0.0		0.0
2022/2021	0.0		0.0		0.0
2021/2020	0.0		0.0		0.0
2020/2019	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	168.8		168.8		461.7
Personal | Other | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	69.1		69.1		626.6
2023/2022	0.0		0.0		0.0
2022/2021	0.0		0.0		0.0
2021/2020	0.0		0.0		0.0
2020/2019	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	$ 69.1		$ 69.1		$ 626.6