Securities (Remaining Maturity of Securities Available for Sale and Held to Maturity) (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Available for Sale - Amortized Cost
ONE YEAR OR LESS	$ 7,886.1
ONE TO FIVE YEARS	21,181.0
FIVE TO TEN YEARS	3,584.9
OVER TEN YEARS	1,450.4
Amortized Cost	34,102.4	$ 29,229.1
Available for Sale - Fair Value
ONE YEAR OR LESS	7,878.2
ONE YEAR OR LESS	21,168.2
FIVE TO TEN YEARS	3,555.3
OVER TEN YEARS	1,434.8
Fair Value	34,036.5	29,001.5
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	7,597.1
ONE TO FIVE YEARS	11,381.7
FIVE TO TEN YEARS	2,845.8
OVER TEN YEARS	1,605.0
Amortized Cost	23,429.6	22,296.7
Held to Maturity - Fair Value
ONE YEAR OR LESS	7,481.0
ONE TO FIVE YEARS	10,967.1
FIVE TO TEN YEARS	2,636.4
OVER TEN YEARS	1,296.7
Fair Value	22,381.2	20,654.5
Amortized Cost
ONE YEAR OR LESS	15,483.2
ONE TO FIVE YEARS	32,562.7
FIVE TO TEN YEARS	6,430.7
OVER TEN YEARS	3,055.4
AMORTIZED COST	57,532.0	51,525.8
Fair Value
ONE YEAR OR LESS	15,359.2
ONE TO FIVE YEARS	32,135.3
FIVE TO TEN YEARS	6,191.7
OVER TEN YEARS	2,731.5
FAIR VALUE	56,417.7	49,656.0
U.S. Government
Available for Sale - Amortized Cost
ONE YEAR OR LESS	1,498.9
ONE TO FIVE YEARS	6,649.1
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Amortized Cost	8,148.0	7,388.9
Available for Sale - Fair Value
ONE YEAR OR LESS	1,505.4
ONE YEAR OR LESS	6,667.0
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Fair Value	8,172.4	7,367.5
Obligations of States and Political Subdivisions
Available for Sale - Amortized Cost
ONE YEAR OR LESS	0.0
ONE TO FIVE YEARS	250.2
FIVE TO TEN YEARS	72.2
OVER TEN YEARS	0.0
Amortized Cost	322.4	311.2
Available for Sale - Fair Value
ONE YEAR OR LESS	0.0
ONE YEAR OR LESS	242.9
FIVE TO TEN YEARS	70.2
OVER TEN YEARS	0.0
Fair Value	313.1	297.6
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	199.9
ONE TO FIVE YEARS	1,426.3
FIVE TO TEN YEARS	802.3
OVER TEN YEARS	29.3
Amortized Cost	2,457.8	2,548.2
Held to Maturity - Fair Value
ONE YEAR OR LESS	199.8
ONE TO FIVE YEARS	1,428.6
FIVE TO TEN YEARS	792.4
OVER TEN YEARS	28.6
Fair Value	2,449.4	2,458.9
Government Sponsored Agency
Available for Sale - Amortized Cost
ONE YEAR OR LESS	4,407.2
ONE TO FIVE YEARS	9,015.5
FIVE TO TEN YEARS	2,145.2
OVER TEN YEARS	1,048.8
Amortized Cost	16,616.7	13,410.5
Available for Sale - Fair Value
ONE YEAR OR LESS	4,401.2
ONE YEAR OR LESS	9,004.0
FIVE TO TEN YEARS	2,129.5
OVER TEN YEARS	1,032.8
Fair Value	16,567.5	13,288.9
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	883.5
ONE TO FIVE YEARS	4,253.8
FIVE TO TEN YEARS	1,906.9
OVER TEN YEARS	1,380.3
Amortized Cost	8,424.5	8,635.0
Held to Maturity - Fair Value
ONE YEAR OR LESS	815.1
ONE TO FIVE YEARS	3,952.2
FIVE TO TEN YEARS	1,717.7
OVER TEN YEARS	1,211.1
Fair Value	7,696.1	7,554.6
Non-U.S. Government
Available for Sale - Amortized Cost
ONE YEAR OR LESS	399.0
ONE TO FIVE YEARS	135.1
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Amortized Cost	534.1	308.9
Available for Sale - Fair Value
ONE YEAR OR LESS	396.6
ONE YEAR OR LESS	130.6
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Fair Value	527.2	296.8
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	3,616.1
ONE TO FIVE YEARS	1,124.9
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Amortized Cost	4,741.0	3,735.8
Held to Maturity - Fair Value
ONE YEAR OR LESS	3,606.5
ONE TO FIVE YEARS	1,107.4
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Fair Value	4,713.9	3,679.7
Corporate Debt
Available for Sale - Amortized Cost
ONE YEAR OR LESS	43.4
ONE TO FIVE YEARS	21.7
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Amortized Cost	65.1	166.6
Available for Sale - Fair Value
ONE YEAR OR LESS	43.1
ONE YEAR OR LESS	21.3
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Fair Value	64.4	163.8
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	207.5
ONE TO FIVE YEARS	181.5
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Amortized Cost	389.0	351.6
Held to Maturity - Fair Value
ONE YEAR OR LESS	204.9
ONE TO FIVE YEARS	179.1
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Fair Value	384.0	340.6
Covered Bonds
Available for Sale - Amortized Cost
ONE YEAR OR LESS	173.5
ONE TO FIVE YEARS	101.8
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Amortized Cost	275.3	234.0
Available for Sale - Fair Value
ONE YEAR OR LESS	173.9
ONE YEAR OR LESS	99.6
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Fair Value	273.5	230.9
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	548.8
ONE TO FIVE YEARS	1,118.3
FIVE TO TEN YEARS	87.4
OVER TEN YEARS	0.0
Amortized Cost	1,754.5	1,776.8
Held to Maturity - Fair Value
ONE YEAR OR LESS	545.9
ONE TO FIVE YEARS	1,080.3
FIVE TO TEN YEARS	87.0
OVER TEN YEARS	0.0
Fair Value	1,713.2	1,714.7
Certificates of Deposit
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	444.5
ONE TO FIVE YEARS	0.0
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Amortized Cost	444.5	336.0
Held to Maturity - Fair Value
ONE YEAR OR LESS	440.5
ONE TO FIVE YEARS	0.0
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Fair Value	440.5	335.7
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Available for Sale - Amortized Cost
ONE YEAR OR LESS	923.1
ONE TO FIVE YEARS	3,877.6
FIVE TO TEN YEARS	202.2
OVER TEN YEARS	0.0
Amortized Cost	5,002.9	4,617.0
Available for Sale - Fair Value
ONE YEAR OR LESS	920.1
ONE YEAR OR LESS	3,870.8
FIVE TO TEN YEARS	193.4
OVER TEN YEARS	0.0
Fair Value	4,984.3	4,583.1
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	1,614.4
ONE TO FIVE YEARS	2,891.1
FIVE TO TEN YEARS	6.0
OVER TEN YEARS	0.0
Amortized Cost	4,511.5	4,146.9
Held to Maturity - Fair Value
ONE YEAR OR LESS	1,587.7
ONE TO FIVE YEARS	2,863.5
FIVE TO TEN YEARS	5.2
OVER TEN YEARS	0.0
Fair Value	4,456.4	3,977.0
Other Asset-Backed
Available for Sale - Amortized Cost
ONE YEAR OR LESS	290.8
ONE TO FIVE YEARS	900.9
FIVE TO TEN YEARS	1,127.2
OVER TEN YEARS	401.6
Amortized Cost	2,720.5	2,188.6
Available for Sale - Fair Value
ONE YEAR OR LESS	288.0
ONE YEAR OR LESS	906.0
FIVE TO TEN YEARS	1,129.1
OVER TEN YEARS	402.0
Fair Value	2,725.1	2,182.7
Held to Maturity - Amortized Cost
Amortized Cost		107.1
Held to Maturity - Fair Value
Fair Value		107.3
Commercial Mortgage-Backed
Available for Sale - Amortized Cost
ONE YEAR OR LESS	150.2
ONE TO FIVE YEARS	229.1
FIVE TO TEN YEARS	38.1
OVER TEN YEARS	0.0
Amortized Cost	417.4	603.4
Available for Sale - Fair Value
ONE YEAR OR LESS	149.9
ONE YEAR OR LESS	226.0
FIVE TO TEN YEARS	33.1
OVER TEN YEARS	0.0
Fair Value	409.0	590.2
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	0.0
ONE TO FIVE YEARS	37.6
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Amortized Cost	37.6	37.6
Held to Maturity - Fair Value
ONE YEAR OR LESS	0.0
ONE TO FIVE YEARS	36.3
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Fair Value	36.3	36.8
Other
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	82.4
ONE TO FIVE YEARS	348.2
FIVE TO TEN YEARS	43.2
OVER TEN YEARS	195.4
Amortized Cost	669.2	621.7
Held to Maturity - Fair Value
ONE YEAR OR LESS	80.6
ONE TO FIVE YEARS	319.7
FIVE TO TEN YEARS	34.1
OVER TEN YEARS	57.0
Fair Value	$ 491.4	$ 449.2