Securities (Reconciliation of Amortized Cost to Fair Value of Available For Sale and Held to Maturity Debt Securities) (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Available for Sale Debt Securities
Amortized Cost	$ 29,229.1	$ 23,659.0
GROSS UNREALIZED GAINS	28.8	13.2
GROSS UNREALIZED LOSSES	256.4	582.4
FAIR VALUE	29,001.5	23,089.8
Held to Maturity Debt Securities
Amortized Cost	22,296.7	26,221.7
GROSS UNREALIZED GAINS	2.9	6.9
GROSS UNREALIZED LOSSES	1,645.1	1,755.6
FAIR VALUE	20,654.5	24,473.0
AMORTIZED COST	51,525.8	49,880.7
GROSS UNREALIZED GAINS	31.7	20.1
GROSS UNREALIZED LOSSES	1,901.5	2,338.0
FAIR VALUE	49,656.0	47,562.8
U.S. Government
Available for Sale Debt Securities
Amortized Cost	7,388.9	3,681.5
GROSS UNREALIZED GAINS	1.5	2.2
GROSS UNREALIZED LOSSES	22.9	61.5
FAIR VALUE	7,367.5	3,622.2
Obligations of States and Political Subdivisions
Available for Sale Debt Securities
Amortized Cost	311.2	315.8
GROSS UNREALIZED GAINS	0.0	0.0
GROSS UNREALIZED LOSSES	13.6	20.0
FAIR VALUE	297.6	295.8
Held to Maturity Debt Securities
Amortized Cost	2,548.2	2,563.9
GROSS UNREALIZED GAINS	0.0	0.5
GROSS UNREALIZED LOSSES	89.3	72.4
FAIR VALUE	2,458.9	2,492.0
Government Sponsored Agency
Available for Sale Debt Securities
Amortized Cost	13,410.5	11,744.3
GROSS UNREALIZED GAINS	10.9	9.0
GROSS UNREALIZED LOSSES	132.5	200.3
FAIR VALUE	13,288.9	11,553.0
Held to Maturity Debt Securities
Amortized Cost	8,635.0	9,355.3
GROSS UNREALIZED GAINS	0.9	2.3
GROSS UNREALIZED LOSSES	1,081.3	1,012.4
FAIR VALUE	7,554.6	8,345.2
Non-U.S. Government
Available for Sale Debt Securities
Amortized Cost	308.9	284.8
GROSS UNREALIZED GAINS	0.2	0.0
GROSS UNREALIZED LOSSES	12.3	20.4
FAIR VALUE	296.8	264.4
Held to Maturity Debt Securities
Amortized Cost	3,735.8	4,789.1
GROSS UNREALIZED GAINS	0.2	0.2
GROSS UNREALIZED LOSSES	56.3	90.7
FAIR VALUE	3,679.7	4,698.6
Corporate Debt
Available for Sale Debt Securities
Amortized Cost	166.6	287.5
GROSS UNREALIZED GAINS	0.1	0.1
GROSS UNREALIZED LOSSES	2.9	8.1
FAIR VALUE	163.8	279.5
Held to Maturity Debt Securities
Amortized Cost	351.6	646.1
GROSS UNREALIZED GAINS	0.0	0.0
GROSS UNREALIZED LOSSES	11.0	28.2
FAIR VALUE	340.6	617.9
Covered Bonds
Available for Sale Debt Securities
Amortized Cost	234.0	356.8
GROSS UNREALIZED GAINS	0.5	0.0
GROSS UNREALIZED LOSSES	3.6	9.7
FAIR VALUE	230.9	347.1
Held to Maturity Debt Securities
Amortized Cost	1,776.8	2,208.6
GROSS UNREALIZED GAINS	0.1	0.3
GROSS UNREALIZED LOSSES	62.2	108.3
FAIR VALUE	1,714.7	2,100.6
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Available for Sale Debt Securities
Amortized Cost	4,617.0	3,013.8
GROSS UNREALIZED GAINS	8.3	0.1
GROSS UNREALIZED LOSSES	42.2	114.0
FAIR VALUE	4,583.1	2,899.9
Held to Maturity Debt Securities
Amortized Cost	4,146.9	5,245.5
GROSS UNREALIZED GAINS	1.4	3.2
GROSS UNREALIZED LOSSES	171.3	294.9
FAIR VALUE	3,977.0	4,953.8
Other Asset-Backed
Available for Sale Debt Securities
Amortized Cost	2,188.6	3,061.0
GROSS UNREALIZED GAINS	7.0	1.6
GROSS UNREALIZED LOSSES	12.9	100.0
FAIR VALUE	2,182.7	2,962.6
Held to Maturity Debt Securities
Amortized Cost	107.1	214.2
GROSS UNREALIZED GAINS	0.3	0.4
GROSS UNREALIZED LOSSES	0.1	0.2
FAIR VALUE	107.3	214.4
Commercial Mortgage-Backed
Available for Sale Debt Securities
Amortized Cost	603.4	913.5
GROSS UNREALIZED GAINS	0.3	0.2
GROSS UNREALIZED LOSSES	13.5	48.4
FAIR VALUE	590.2	865.3
Held to Maturity Debt Securities
Amortized Cost	37.6	37.6
GROSS UNREALIZED GAINS	0.0	0.0
GROSS UNREALIZED LOSSES	0.8	0.8
FAIR VALUE	36.8	36.8
Certificates of Deposit
Held to Maturity Debt Securities
Amortized Cost	336.0	585.1
GROSS UNREALIZED GAINS	0.0	0.0
GROSS UNREALIZED LOSSES	0.3	0.7
FAIR VALUE	335.7	584.4
Other
Held to Maturity Debt Securities
Amortized Cost	621.7	576.3
GROSS UNREALIZED GAINS	0.0	0.0
GROSS UNREALIZED LOSSES	172.5	147.0
FAIR VALUE	$ 449.2	$ 429.3