Securities (Reconciliation of Amortized Cost to Fair Value of Available For Sale and Held to Maturity Debt Securities) (Details) - USD ($) $ in Millions	Jun. 30, 2026	Dec. 31, 2025
Available for Sale Debt Securities
AMORTIZED COST	$ 38,198.3	$ 34,102.4
GROSS UNREALIZED GAINS	53.7	92.8
GROSS UNREALIZED LOSSES	128.9	158.7
FAIR VALUE	38,123.1	34,036.5
Held to Maturity Debt Securities
AMORTIZED COST	23,492.1	23,429.6
GROSS UNREALIZED GAINS	5.1	17.4
GROSS UNREALIZED LOSSES	1,143.7	1,065.8
FAIR VALUE	22,353.5	22,381.2
TOTAL	61,690.4	57,532.0
GROSS UNREALIZED GAINS	58.8	110.2
GROSS UNREALIZED LOSSES	1,272.6	1,224.5
TOTAL	60,476.6	56,417.7
U.S. Governments
Available for Sale Debt Securities
AMORTIZED COST	7,872.2	8,148.0
GROSS UNREALIZED GAINS	13.1	29.5
GROSS UNREALIZED LOSSES	2.0	5.1
FAIR VALUE	7,883.3	8,172.4
Obligations of States and Political Subdivisions
Available for Sale Debt Securities
AMORTIZED COST		322.4
GROSS UNREALIZED GAINS		0.0
GROSS UNREALIZED LOSSES		9.3
FAIR VALUE		313.1
Held to Maturity Debt Securities
AMORTIZED COST	2,384.8	2,457.8
GROSS UNREALIZED GAINS	1.0	4.6
GROSS UNREALIZED LOSSES	38.3	13.0
FAIR VALUE	2,347.5	2,449.4
Government Sponsored Agency
Available for Sale Debt Securities
AMORTIZED COST	19,381.1	16,616.7
GROSS UNREALIZED GAINS	26.6	44.1
GROSS UNREALIZED LOSSES	104.9	93.3
FAIR VALUE	19,302.8	16,567.5
Held to Maturity Debt Securities
AMORTIZED COST	8,112.8	8,424.5
GROSS UNREALIZED GAINS	1.9	8.3
GROSS UNREALIZED LOSSES	804.9	736.7
FAIR VALUE	7,309.8	7,696.1
Non-U.S. Government
Available for Sale Debt Securities
AMORTIZED COST	409.0	534.1
GROSS UNREALIZED GAINS	0.6	0.0
GROSS UNREALIZED LOSSES	1.1	6.9
FAIR VALUE	408.5	527.2
Held to Maturity Debt Securities
AMORTIZED COST	4,561.2	4,741.0
GROSS UNREALIZED GAINS	1.4	0.1
GROSS UNREALIZED LOSSES	22.0	27.2
FAIR VALUE	4,540.6	4,713.9
Corporate Debt
Available for Sale Debt Securities
AMORTIZED COST	271.2	65.1
GROSS UNREALIZED GAINS	0.7	0.0
GROSS UNREALIZED LOSSES	0.5	0.7
FAIR VALUE	271.4	64.4
Held to Maturity Debt Securities
AMORTIZED COST	280.3	389.0
GROSS UNREALIZED GAINS	0.0	0.0
GROSS UNREALIZED LOSSES	4.2	5.0
FAIR VALUE	276.1	384.0
Covered Bonds
Available for Sale Debt Securities
AMORTIZED COST	277.4	275.3
GROSS UNREALIZED GAINS	0.2	0.4
GROSS UNREALIZED LOSSES	1.9	2.2
FAIR VALUE	275.7	273.5
Held to Maturity Debt Securities
AMORTIZED COST	2,114.9	1,754.5
GROSS UNREALIZED GAINS	0.1	0.1
GROSS UNREALIZED LOSSES	40.3	41.4
FAIR VALUE	2,074.7	1,713.2
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Available for Sale Debt Securities
AMORTIZED COST	4,674.2	5,002.9
GROSS UNREALIZED GAINS	8.3	11.0
GROSS UNREALIZED LOSSES	12.1	29.6
FAIR VALUE	4,670.4	4,984.3
Held to Maturity Debt Securities
AMORTIZED COST	4,595.4	4,511.5
GROSS UNREALIZED GAINS	0.6	4.3
GROSS UNREALIZED LOSSES	56.4	59.4
FAIR VALUE	4,539.6	4,456.4
CLOs
Available for Sale Debt Securities
AMORTIZED COST	3,451.7	2,151.3
GROSS UNREALIZED GAINS	2.3	3.7
GROSS UNREALIZED LOSSES	0.3	0.1
FAIR VALUE	3,453.7	2,154.9
Other Asset-Backed
Available for Sale Debt Securities
AMORTIZED COST	1,349.8	569.2
GROSS UNREALIZED GAINS	1.5	4.0
GROSS UNREALIZED LOSSES	5.6	3.0
FAIR VALUE	1,345.7	570.2
Held to Maturity Debt Securities
AMORTIZED COST	47.1
GROSS UNREALIZED GAINS	0.0
GROSS UNREALIZED LOSSES	0.0
FAIR VALUE	47.1
Commercial Mortgage-Backed
Available for Sale Debt Securities
AMORTIZED COST	511.7	417.4
GROSS UNREALIZED GAINS	0.4	0.1
GROSS UNREALIZED LOSSES	0.5	8.5
FAIR VALUE	511.6	409.0
Held to Maturity Debt Securities
AMORTIZED COST	37.6	37.6
GROSS UNREALIZED GAINS	0.0	0.0
GROSS UNREALIZED LOSSES	1.8	1.3
FAIR VALUE	35.8	36.3
Certificate of Deposit
Held to Maturity Debt Securities
AMORTIZED COST	751.8	444.5
GROSS UNREALIZED GAINS	0.1	0.0
GROSS UNREALIZED LOSSES	0.1	4.0
FAIR VALUE	751.8	440.5
Other
Held to Maturity Debt Securities
AMORTIZED COST	606.2	669.2
GROSS UNREALIZED GAINS	0.0	0.0
GROSS UNREALIZED LOSSES	175.7	177.8
FAIR VALUE	$ 430.5	$ 491.4