Securities (Reconciliation of Amortized Cost to Fair Value of Securities Held to Maturity) (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 23,564.5	$ 17,791.1
GROSS UNREALIZED GAINS	34.5	84.3
GROSS UNREALIZED LOSSES	283.6	78.0
FAIR VALUE	23,315.4	17,797.4
U.S. Government
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	47.0	90.0
GROSS UNREALIZED GAINS	0.0	0.0
GROSS UNREALIZED LOSSES	0.0	0.0
FAIR VALUE	47.0	90.0
Obligations of States and Political Subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	0.8	2.1
GROSS UNREALIZED GAINS	0.0	0.1
GROSS UNREALIZED LOSSES	0.0	0.0
FAIR VALUE	0.8	2.2
Government Sponsored Agency
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	5,927.6	3.0
GROSS UNREALIZED GAINS	1.1	0.3
GROSS UNREALIZED LOSSES	106.1	0.0
FAIR VALUE	5,822.6	3.3
Non-U.S. Government
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	5,773.3	8,336.6
GROSS UNREALIZED GAINS	3.9	7.3
GROSS UNREALIZED LOSSES	9.8	0.2
FAIR VALUE	5,767.4	8,343.7
Corporate Debt
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	901.8	588.0
GROSS UNREALIZED GAINS	2.5	6.5
GROSS UNREALIZED LOSSES	6.5	0.1
FAIR VALUE	897.8	594.4
Covered Bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	2,942.4	3,184.6
GROSS UNREALIZED GAINS	8.3	24.6
GROSS UNREALIZED LOSSES	9.6	0.3
FAIR VALUE	2,941.1	3,208.9
Certificates of Deposit
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	674.7	807.2
GROSS UNREALIZED GAINS	0.0	0.0
GROSS UNREALIZED LOSSES	0.0	0.0
FAIR VALUE	674.7	807.2
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	6,098.0	3,648.0
GROSS UNREALIZED GAINS	14.3	43.5
GROSS UNREALIZED LOSSES	80.0	0.9
FAIR VALUE	6,032.3	3,690.6
Other Asset-Backed
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	682.6	677.0
GROSS UNREALIZED GAINS	1.0	0.9
GROSS UNREALIZED LOSSES	0.0	0.0
FAIR VALUE	683.6	677.9
Other
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	516.3	454.6
GROSS UNREALIZED GAINS	3.4	1.1
GROSS UNREALIZED LOSSES	71.6	76.5
FAIR VALUE	$ 448.1	$ 379.2

Amount excluding accrued interest, before allowance for credit loss, of investment in debt security measured at amortized cost (held-to-maturity).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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