Securities (Reconciliation of Amortized Cost to Fair Value of Securities Held to Maturity) (Details) - USD ($) $ in Millions	Jun. 30, 2022	Dec. 31, 2021
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 20,112.6	$ 23,564.5
GROSS UNREALIZED GAINS	2.6	34.5
GROSS UNREALIZED LOSSES	1,189.7	283.6
FAIR VALUE	18,925.5	23,315.4
U.S. Government
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	56.9	47.0
GROSS UNREALIZED GAINS	0.1	0.0
GROSS UNREALIZED LOSSES	0.5	0.0
FAIR VALUE	56.5	47.0
Obligations of States and Political Subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost		0.8
GROSS UNREALIZED GAINS		0.0
GROSS UNREALIZED LOSSES		0.0
FAIR VALUE		0.8
Government Sponsored Agency
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	5,806.7	5,927.6
GROSS UNREALIZED GAINS	0.1	1.1
GROSS UNREALIZED LOSSES	582.5	106.1
FAIR VALUE	5,224.3	5,822.6
Non-U.S. Government
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	3,097.0	5,773.3
GROSS UNREALIZED GAINS	0.1	3.9
GROSS UNREALIZED LOSSES	79.5	9.8
FAIR VALUE	3,017.6	5,767.4
Corporate Debt
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	873.2	901.8
GROSS UNREALIZED GAINS	0.0	2.5
GROSS UNREALIZED LOSSES	32.6	6.5
FAIR VALUE	840.6	897.8
Covered Bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	2,678.3	2,942.4
GROSS UNREALIZED GAINS	0.4	8.3
GROSS UNREALIZED LOSSES	101.5	9.6
FAIR VALUE	2,577.2	2,941.1
Certificates of Deposit
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	554.3	674.7
GROSS UNREALIZED GAINS	0.0	0.0
GROSS UNREALIZED LOSSES	0.0	0.0
FAIR VALUE	554.3	674.7
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	6,065.8	6,098.0
GROSS UNREALIZED GAINS	1.9	14.3
GROSS UNREALIZED LOSSES	273.6	80.0
FAIR VALUE	5,794.1	6,032.3
Other Asset-Backed
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	496.1	682.6
GROSS UNREALIZED GAINS	0.0	1.0
GROSS UNREALIZED LOSSES	1.4	0.0
FAIR VALUE	494.7	683.6
Other
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	484.3	516.3
GROSS UNREALIZED GAINS	0.0	3.4
GROSS UNREALIZED LOSSES	118.1	71.6
FAIR VALUE	$ 366.2	$ 448.1