Securities (Reconciliation of Amortized Cost to Fair Value of Available For Sale and Held to Maturity Debt Securities) (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Available for Sale
Amortized Cost	$ 34,102.4	$ 29,229.1
GROSS UNREALIZED GAINS	92.8	28.8
GROSS UNREALIZED LOSSES	158.7	256.4
FAIR VALUE	34,036.5	29,001.5
Held to Maturity
Amortized Cost	23,429.6	22,296.7
GROSS UNREALIZED GAINS	17.4	2.9
GROSS UNREALIZED LOSSES	1,065.8	1,645.1
FAIR VALUE	22,381.2	20,654.5
AMORTIZED COST	57,532.0	51,525.8
GROSS UNREALIZED GAINS	110.2	31.7
GROSS UNREALIZED LOSSES	1,224.5	1,901.5
FAIR VALUE	56,417.7	49,656.0
U.S. Government
Available for Sale
Amortized Cost	8,148.0	7,388.9
GROSS UNREALIZED GAINS	29.5	1.5
GROSS UNREALIZED LOSSES	5.1	22.9
FAIR VALUE	8,172.4	7,367.5
Obligations of States and Political Subdivisions
Available for Sale
Amortized Cost	322.4	311.2
GROSS UNREALIZED GAINS	0.0	0.0
GROSS UNREALIZED LOSSES	9.3	13.6
FAIR VALUE	313.1	297.6
Held to Maturity
Amortized Cost	2,457.8	2,548.2
GROSS UNREALIZED GAINS	4.6	0.0
GROSS UNREALIZED LOSSES	13.0	89.3
FAIR VALUE	2,449.4	2,458.9
Government Sponsored Agency
Available for Sale
Amortized Cost	16,616.7	13,410.5
GROSS UNREALIZED GAINS	44.1	10.9
GROSS UNREALIZED LOSSES	93.3	132.5
FAIR VALUE	16,567.5	13,288.9
Held to Maturity
Amortized Cost	8,424.5	8,635.0
GROSS UNREALIZED GAINS	8.3	0.9
GROSS UNREALIZED LOSSES	736.7	1,081.3
FAIR VALUE	7,696.1	7,554.6
Non-U.S. Government
Available for Sale
Amortized Cost	534.1	308.9
GROSS UNREALIZED GAINS	0.0	0.2
GROSS UNREALIZED LOSSES	6.9	12.3
FAIR VALUE	527.2	296.8
Held to Maturity
Amortized Cost	4,741.0	3,735.8
GROSS UNREALIZED GAINS	0.1	0.2
GROSS UNREALIZED LOSSES	27.2	56.3
FAIR VALUE	4,713.9	3,679.7
Corporate Debt
Available for Sale
Amortized Cost	65.1	166.6
GROSS UNREALIZED GAINS	0.0	0.1
GROSS UNREALIZED LOSSES	0.7	2.9
FAIR VALUE	64.4	163.8
Held to Maturity
Amortized Cost	389.0	351.6
GROSS UNREALIZED GAINS	0.0	0.0
GROSS UNREALIZED LOSSES	5.0	11.0
FAIR VALUE	384.0	340.6
Covered Bonds
Available for Sale
Amortized Cost	275.3	234.0
GROSS UNREALIZED GAINS	0.4	0.5
GROSS UNREALIZED LOSSES	2.2	3.6
FAIR VALUE	273.5	230.9
Held to Maturity
Amortized Cost	1,754.5	1,776.8
GROSS UNREALIZED GAINS	0.1	0.1
GROSS UNREALIZED LOSSES	41.4	62.2
FAIR VALUE	1,713.2	1,714.7
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Available for Sale
Amortized Cost	5,002.9	4,617.0
GROSS UNREALIZED GAINS	11.0	8.3
GROSS UNREALIZED LOSSES	29.6	42.2
FAIR VALUE	4,984.3	4,583.1
Held to Maturity
Amortized Cost	4,511.5	4,146.9
GROSS UNREALIZED GAINS	4.3	1.4
GROSS UNREALIZED LOSSES	59.4	171.3
FAIR VALUE	4,456.4	3,977.0
Other Asset-Backed
Available for Sale
Amortized Cost	2,720.5	2,188.6
GROSS UNREALIZED GAINS	7.7	7.0
GROSS UNREALIZED LOSSES	3.1	12.9
FAIR VALUE	2,725.1	2,182.7
Held to Maturity
Amortized Cost		107.1
GROSS UNREALIZED GAINS		0.3
GROSS UNREALIZED LOSSES		0.1
FAIR VALUE		107.3
Commercial Mortgage-Backed
Available for Sale
Amortized Cost	417.4	603.4
GROSS UNREALIZED GAINS	0.1	0.3
GROSS UNREALIZED LOSSES	8.5	13.5
FAIR VALUE	409.0	590.2
Held to Maturity
Amortized Cost	37.6	37.6
GROSS UNREALIZED GAINS	0.0	0.0
GROSS UNREALIZED LOSSES	1.3	0.8
FAIR VALUE	36.3	36.8
Certificates of Deposit
Held to Maturity
Amortized Cost	444.5	336.0
GROSS UNREALIZED GAINS	0.0	0.0
GROSS UNREALIZED LOSSES	4.0	0.3
FAIR VALUE	440.5	335.7
Other
Held to Maturity
Amortized Cost	669.2	621.7
GROSS UNREALIZED GAINS	0.0	0.0
GROSS UNREALIZED LOSSES	177.8	172.5
FAIR VALUE	$ 491.4	$ 449.2