Securities (Reconciliation of Amortized Cost to Fair Value of Securities Held to Maturity) (Details) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 25,249.8	$ 23,564.5
GROSS UNREALIZED GAINS	1.4	34.5
GROSS UNREALIZED LOSSES	2,186.3	283.6
FAIR VALUE	23,064.9	23,315.4
U.S. Government
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	57.9	47.0
GROSS UNREALIZED GAINS	0.0	0.0
GROSS UNREALIZED LOSSES	0.0	0.0
FAIR VALUE	57.9	47.0
Obligations of States and Political Subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	2,558.5	0.8
GROSS UNREALIZED GAINS	0.0	0.0
GROSS UNREALIZED LOSSES	133.5	0.0
FAIR VALUE	2,425.0	0.8
Government Sponsored Agency
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	9,627.1	5,927.6
GROSS UNREALIZED GAINS	0.0	1.1
GROSS UNREALIZED LOSSES	1,049.2	106.1
FAIR VALUE	8,577.9	5,822.6
Non-U.S. Government
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	2,844.9	5,773.3
GROSS UNREALIZED GAINS	0.1	3.9
GROSS UNREALIZED LOSSES	134.3	9.8
FAIR VALUE	2,710.7	5,767.4
Corporate Debt
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	798.2	901.8
GROSS UNREALIZED GAINS	0.0	2.5
GROSS UNREALIZED LOSSES	48.6	6.5
FAIR VALUE	749.6	897.8
Covered Bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	2,466.3	2,942.4
GROSS UNREALIZED GAINS	0.1	8.3
GROSS UNREALIZED LOSSES	144.5	9.6
FAIR VALUE	2,321.9	2,941.1
Certificates of Deposit
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	475.5	674.7
GROSS UNREALIZED GAINS	0.1	0.0
GROSS UNREALIZED LOSSES	33.3	0.0
FAIR VALUE	442.3	674.7
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	5,621.8	6,098.0
GROSS UNREALIZED GAINS	1.1	14.3
GROSS UNREALIZED LOSSES	491.4	80.0
FAIR VALUE	5,131.5	6,032.3
Other Asset-Backed
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	292.2	682.6
GROSS UNREALIZED GAINS	0.0	1.0
GROSS UNREALIZED LOSSES	1.4	0.0
FAIR VALUE	290.8	683.6
Other
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	507.4	516.3
GROSS UNREALIZED GAINS	0.0	3.4
GROSS UNREALIZED LOSSES	150.1	71.6
FAIR VALUE	$ 357.3	$ 448.1