Securities (Reconciliation of Amortized Cost to Fair Value of Securities Held to Maturity) (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 25,036.1	$ 23,564.5
GROSS UNREALIZED GAINS	1.4	34.5
GROSS UNREALIZED LOSSES	2,158.2	283.6
FAIR VALUE	22,879.3	23,315.4
U.S. Government
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	50.0	47.0
GROSS UNREALIZED GAINS	0.0	0.0
GROSS UNREALIZED LOSSES	0.0	0.0
FAIR VALUE	50.0	47.0
Obligations of States and Political Subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	2,565.3	0.8
GROSS UNREALIZED GAINS	0.0	0.0
GROSS UNREALIZED LOSSES	149.8	0.0
FAIR VALUE	2,415.5	0.8
Government Sponsored Agency
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	9,407.7	5,927.6
GROSS UNREALIZED GAINS	0.0	1.1
GROSS UNREALIZED LOSSES	1,076.0	106.1
FAIR VALUE	8,331.7	5,822.6
Non-U.S. Government
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	3,234.0	5,773.3
GROSS UNREALIZED GAINS	0.1	3.9
GROSS UNREALIZED LOSSES	133.8	9.8
FAIR VALUE	3,100.3	5,767.4
Corporate Debt
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	713.3	901.8
GROSS UNREALIZED GAINS	0.0	2.5
GROSS UNREALIZED LOSSES	45.4	6.5
FAIR VALUE	667.9	897.8
Covered Bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	2,530.3	2,942.4
GROSS UNREALIZED GAINS	0.3	8.3
GROSS UNREALIZED LOSSES	158.7	9.6
FAIR VALUE	2,371.9	2,941.1
Certificates of Deposit
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	35.9	674.7
GROSS UNREALIZED GAINS	0.0	0.0
GROSS UNREALIZED LOSSES	0.0	0.0
FAIR VALUE	35.9	674.7
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	5,703.3	6,098.0
GROSS UNREALIZED GAINS	1.0	14.3
GROSS UNREALIZED LOSSES	436.1	80.0
FAIR VALUE	5,268.2	6,032.3
Other Asset-Backed
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	263.7	682.6
GROSS UNREALIZED GAINS	0.0	1.0
GROSS UNREALIZED LOSSES	1.0	0.0
FAIR VALUE	262.7	683.6
Other
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	532.6	516.3
GROSS UNREALIZED GAINS	0.0	3.4
GROSS UNREALIZED LOSSES	157.4	71.6
FAIR VALUE	$ 375.2	$ 448.1