Securities (Reconciliation of Amortized Cost to Fair Value of Available For Sale and Held to Maturity Debt Securities) (Details) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025
Available for Sale Debt Securities
AMORTIZED COST	$ 37,065.7	$ 34,102.4
GROSS UNREALIZED GAINS	51.4	92.8
GROSS UNREALIZED LOSSES	203.9	158.7
FAIR VALUE	36,913.2	34,036.5
Held to Maturity Debt Securities
AMORTIZED COST	24,286.2	23,429.6
GROSS UNREALIZED GAINS	7.2	17.4
GROSS UNREALIZED LOSSES	1,155.4	1,065.8
FAIR VALUE	23,138.0	22,381.2
TOTAL	61,351.9	57,532.0
GROSS UNREALIZED GAINS	58.6	110.2
GROSS UNREALIZED LOSSES	1,359.3	1,224.5
TOTAL	60,051.2	56,417.7
U.S. Governments
Available for Sale Debt Securities
AMORTIZED COST	7,965.3	8,148.0
GROSS UNREALIZED GAINS	11.9	29.5
GROSS UNREALIZED LOSSES	5.3	5.1
FAIR VALUE	7,971.9	8,172.4
Obligations of States and Political Subdivisions
Available for Sale Debt Securities
AMORTIZED COST	321.0	322.4
GROSS UNREALIZED GAINS	0.0	0.0
GROSS UNREALIZED LOSSES	9.1	9.3
FAIR VALUE	311.9	313.1
Held to Maturity Debt Securities
AMORTIZED COST	2,442.1	2,457.8
GROSS UNREALIZED GAINS	1.7	4.6
GROSS UNREALIZED LOSSES	22.9	13.0
FAIR VALUE	2,420.9	2,449.4
Government Sponsored Agency
Available for Sale Debt Securities
AMORTIZED COST	18,614.1	16,616.7
GROSS UNREALIZED GAINS	29.2	44.1
GROSS UNREALIZED LOSSES	114.2	93.3
FAIR VALUE	18,529.1	16,567.5
Held to Maturity Debt Securities
AMORTIZED COST	8,299.6	8,424.5
GROSS UNREALIZED GAINS	4.1	8.3
GROSS UNREALIZED LOSSES	775.4	736.7
FAIR VALUE	7,528.3	7,696.1
Non-U.S. Government
Available for Sale Debt Securities
AMORTIZED COST	318.3	534.1
GROSS UNREALIZED GAINS	0.0	0.0
GROSS UNREALIZED LOSSES	6.7	6.9
FAIR VALUE	311.6	527.2
Held to Maturity Debt Securities
AMORTIZED COST	5,026.8	4,741.0
GROSS UNREALIZED GAINS	0.2	0.1
GROSS UNREALIZED LOSSES	33.0	27.2
FAIR VALUE	4,994.0	4,713.9
Corporate Debt
Available for Sale Debt Securities
AMORTIZED COST	66.9	65.1
GROSS UNREALIZED GAINS	0.0	0.0
GROSS UNREALIZED LOSSES	0.8	0.7
FAIR VALUE	66.1	64.4
Held to Maturity Debt Securities
AMORTIZED COST	303.5	389.0
GROSS UNREALIZED GAINS	0.0	0.0
GROSS UNREALIZED LOSSES	6.0	5.0
FAIR VALUE	297.5	384.0
Covered Bonds
Available for Sale Debt Securities
AMORTIZED COST	277.4	275.3
GROSS UNREALIZED GAINS	0.3	0.4
GROSS UNREALIZED LOSSES	2.7	2.2
FAIR VALUE	275.0	273.5
Held to Maturity Debt Securities
AMORTIZED COST	2,192.8	1,754.5
GROSS UNREALIZED GAINS	0.0	0.1
GROSS UNREALIZED LOSSES	52.8	41.4
FAIR VALUE	2,140.0	1,713.2
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Available for Sale Debt Securities
AMORTIZED COST	5,057.0	5,002.9
GROSS UNREALIZED GAINS	7.8	11.0
GROSS UNREALIZED LOSSES	50.1	29.6
FAIR VALUE	5,014.7	4,984.3
Held to Maturity Debt Securities
AMORTIZED COST	4,604.9	4,511.5
GROSS UNREALIZED GAINS	1.2	4.3
GROSS UNREALIZED LOSSES	78.4	59.4
FAIR VALUE	4,527.7	4,456.4
CLOs
Available for Sale Debt Securities
AMORTIZED COST	3,295.2	2,151.3
GROSS UNREALIZED GAINS	0.4	3.7
GROSS UNREALIZED LOSSES	2.2	0.1
FAIR VALUE	3,293.4	2,154.9
Other Asset-Backed
Available for Sale Debt Securities
AMORTIZED COST	705.3	569.2
GROSS UNREALIZED GAINS	1.8	4.0
GROSS UNREALIZED LOSSES	3.7	3.0
FAIR VALUE	703.4	570.2
Commercial Mortgage-Backed
Available for Sale Debt Securities
AMORTIZED COST	445.2	417.4
GROSS UNREALIZED GAINS	0.0	0.1
GROSS UNREALIZED LOSSES	9.1	8.5
FAIR VALUE	436.1	409.0
Held to Maturity Debt Securities
AMORTIZED COST	37.6	37.6
GROSS UNREALIZED GAINS	0.0	0.0
GROSS UNREALIZED LOSSES	1.3	1.3
FAIR VALUE	36.3	36.3
Certificate of Deposit
Held to Maturity Debt Securities
AMORTIZED COST	766.5	444.5
GROSS UNREALIZED GAINS	0.0	0.0
GROSS UNREALIZED LOSSES	3.7	4.0
FAIR VALUE	762.8	440.5
Other
Held to Maturity Debt Securities
AMORTIZED COST	612.4	669.2
GROSS UNREALIZED GAINS	0.0	0.0
GROSS UNREALIZED LOSSES	181.9	177.8
FAIR VALUE	$ 430.5	$ 491.4