Securities (Remaining Maturity of Securities Available for Sale and Held to Maturity) (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Available for Sale - Amortized Cost
ONE YEAR OR LESS	$ 3,877.8
ONE TO FIVE YEARS	19,519.1
FIVE TO TEN YEARS	4,922.2
OVER TEN YEARS	910.0
Amortized Cost	29,229.1	$ 23,659.0
Available for Sale - Fair Value
ONE YEAR OR LESS	3,850.7
ONE YEAR OR LESS	19,387.0
FIVE TO TEN YEARS	4,875.0
OVER TEN YEARS	888.8
Fair Value	29,001.5	23,089.8
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	6,842.3
ONE TO FIVE YEARS	9,617.0
FIVE TO TEN YEARS	3,887.2
OVER TEN YEARS	1,950.2
Amortized Cost	22,296.7	26,221.7
Held to Maturity - Fair Value
ONE YEAR OR LESS	6,689.9
ONE TO FIVE YEARS	8,930.5
FIVE TO TEN YEARS	3,474.4
OVER TEN YEARS	1,559.7
Fair Value	20,654.5	24,473.0
Amortized Cost
ONE YEAR OR LESS	10,720.1
ONE TO FIVE YEARS	29,136.1
FIVE TO TEN YEARS	8,809.4
OVER TEN YEARS	2,860.2
AMORTIZED COST	51,525.8	49,880.7
Fair Value
ONE YEAR OR LESS	10,540.6
ONE TO FIVE YEARS	28,317.5
FIVE TO TEN YEARS	8,349.4
OVER TEN YEARS	2,448.5
FAIR VALUE	49,656.0	47,562.8
U.S. Government
Available for Sale - Amortized Cost
ONE YEAR OR LESS	397.4
ONE TO FIVE YEARS	5,326.2
FIVE TO TEN YEARS	1,665.3
OVER TEN YEARS	0.0
Amortized Cost	7,388.9	3,681.5
Available for Sale - Fair Value
ONE YEAR OR LESS	396.2
ONE YEAR OR LESS	5,309.3
FIVE TO TEN YEARS	1,662.0
OVER TEN YEARS	0.0
Fair Value	7,367.5	3,622.2
Obligations of States and Political Subdivisions
Available for Sale - Amortized Cost
ONE YEAR OR LESS	0.0
ONE TO FIVE YEARS	242.5
FIVE TO TEN YEARS	68.7
OVER TEN YEARS	0.0
Amortized Cost	311.2	315.8
Available for Sale - Fair Value
ONE YEAR OR LESS	0.0
ONE YEAR OR LESS	232.0
FIVE TO TEN YEARS	65.6
OVER TEN YEARS	0.0
Fair Value	297.6	295.8
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	115.3
ONE TO FIVE YEARS	1,387.7
FIVE TO TEN YEARS	892.9
OVER TEN YEARS	152.3
Amortized Cost	2,548.2	2,563.9
Held to Maturity - Fair Value
ONE YEAR OR LESS	114.7
ONE TO FIVE YEARS	1,357.2
FIVE TO TEN YEARS	845.8
OVER TEN YEARS	141.2
Fair Value	2,458.9	2,492.0
Government Sponsored Agency
Available for Sale - Amortized Cost
ONE YEAR OR LESS	3,087.3
ONE TO FIVE YEARS	7,129.2
FIVE TO TEN YEARS	2,389.5
OVER TEN YEARS	804.5
Amortized Cost	13,410.5	11,744.3
Available for Sale - Fair Value
ONE YEAR OR LESS	3,065.5
ONE YEAR OR LESS	7,077.9
FIVE TO TEN YEARS	2,362.9
OVER TEN YEARS	782.6
Fair Value	13,288.9	11,553.0
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	888.5
ONE TO FIVE YEARS	3,358.8
FIVE TO TEN YEARS	2,771.9
OVER TEN YEARS	1,615.8
Amortized Cost	8,635.0	9,355.3
Held to Maturity - Fair Value
ONE YEAR OR LESS	793.6
ONE TO FIVE YEARS	2,971.4
FIVE TO TEN YEARS	2,426.5
OVER TEN YEARS	1,363.1
Fair Value	7,554.6	8,345.2
Non-U.S. Government
Available for Sale - Amortized Cost
ONE YEAR OR LESS	0.0
ONE TO FIVE YEARS	308.9
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Amortized Cost	308.9	284.8
Available for Sale - Fair Value
ONE YEAR OR LESS	0.0
ONE YEAR OR LESS	296.8
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Fair Value	296.8	264.4
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	2,697.3
ONE TO FIVE YEARS	1,038.5
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Amortized Cost	3,735.8	4,789.1
Held to Maturity - Fair Value
ONE YEAR OR LESS	2,696.6
ONE TO FIVE YEARS	983.1
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Fair Value	3,679.7	4,698.6
Corporate Debt
Available for Sale - Amortized Cost
ONE YEAR OR LESS	126.4
ONE TO FIVE YEARS	40.2
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Amortized Cost	166.6	287.5
Available for Sale - Fair Value
ONE YEAR OR LESS	124.9
ONE YEAR OR LESS	38.9
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Fair Value	163.8	279.5
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	142.3
ONE TO FIVE YEARS	194.7
FIVE TO TEN YEARS	14.6
OVER TEN YEARS	0.0
Amortized Cost	351.6	646.1
Held to Maturity - Fair Value
ONE YEAR OR LESS	140.4
ONE TO FIVE YEARS	187.5
FIVE TO TEN YEARS	12.7
OVER TEN YEARS	0.0
Fair Value	340.6	617.9
Covered Bonds
Available for Sale - Amortized Cost
ONE YEAR OR LESS	0.0
ONE TO FIVE YEARS	234.0
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Amortized Cost	234.0	356.8
Available for Sale - Fair Value
ONE YEAR OR LESS	0.0
ONE YEAR OR LESS	230.9
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Fair Value	230.9	347.1
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	475.3
ONE TO FIVE YEARS	1,178.7
FIVE TO TEN YEARS	122.8
OVER TEN YEARS	0.0
Amortized Cost	1,776.8	2,208.6
Held to Maturity - Fair Value
ONE YEAR OR LESS	473.8
ONE TO FIVE YEARS	1,123.8
FIVE TO TEN YEARS	117.1
OVER TEN YEARS	0.0
Fair Value	1,714.7	2,100.6
Certificates of Deposit
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	336.0
ONE TO FIVE YEARS	0.0
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Amortized Cost	336.0	585.1
Held to Maturity - Fair Value
ONE YEAR OR LESS	335.7
ONE TO FIVE YEARS	0.0
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Fair Value	335.7	584.4
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Available for Sale - Amortized Cost
ONE YEAR OR LESS	171.2
ONE TO FIVE YEARS	4,152.0
FIVE TO TEN YEARS	293.8
OVER TEN YEARS	0.0
Amortized Cost	4,617.0	3,013.8
Available for Sale - Fair Value
ONE YEAR OR LESS	169.6
ONE YEAR OR LESS	4,129.9
FIVE TO TEN YEARS	283.6
OVER TEN YEARS	0.0
Fair Value	4,583.1	2,899.9
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	2,126.2
ONE TO FIVE YEARS	2,015.4
FIVE TO TEN YEARS	5.3
OVER TEN YEARS	0.0
Amortized Cost	4,146.9	5,245.5
Held to Maturity - Fair Value
ONE YEAR OR LESS	2,075.0
ONE TO FIVE YEARS	1,897.5
FIVE TO TEN YEARS	4.5
OVER TEN YEARS	0.0
Fair Value	3,977.0	4,953.8
Other Asset-Backed
Available for Sale - Amortized Cost
ONE YEAR OR LESS	50.4
ONE TO FIVE YEARS	1,561.5
FIVE TO TEN YEARS	471.2
OVER TEN YEARS	105.5
Amortized Cost	2,188.6	3,061.0
Available for Sale - Fair Value
ONE YEAR OR LESS	49.7
ONE YEAR OR LESS	1,552.7
FIVE TO TEN YEARS	474.1
OVER TEN YEARS	106.2
Fair Value	2,182.7	2,962.6
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	0.0
ONE TO FIVE YEARS	77.8
FIVE TO TEN YEARS	29.3
OVER TEN YEARS	0.0
Amortized Cost	107.1	214.2
Held to Maturity - Fair Value
ONE YEAR OR LESS	0.0
ONE TO FIVE YEARS	78.1
FIVE TO TEN YEARS	29.2
OVER TEN YEARS	0.0
Fair Value	107.3	214.4
Commercial Mortgage-Backed
Available for Sale - Amortized Cost
ONE YEAR OR LESS	45.1
ONE TO FIVE YEARS	524.6
FIVE TO TEN YEARS	33.7
OVER TEN YEARS	0.0
Amortized Cost	603.4	913.5
Available for Sale - Fair Value
ONE YEAR OR LESS	44.8
ONE YEAR OR LESS	518.6
FIVE TO TEN YEARS	26.8
OVER TEN YEARS	0.0
Fair Value	590.2	865.3
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	36.8
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Fair Value	36.8	36.8
Other
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	61.4
ONE TO FIVE YEARS	327.8
FIVE TO TEN YEARS	50.4
OVER TEN YEARS	182.1
Amortized Cost	621.7	576.3
Held to Maturity - Fair Value
ONE YEAR OR LESS	60.1
ONE TO FIVE YEARS	295.1
FIVE TO TEN YEARS	38.6
OVER TEN YEARS	55.4
Fair Value	$ 449.2	$ 429.3