Securities (Narrative) (Details) $ in Millions	3 Months Ended	12 Months Ended
Dec. 31, 2022 USD ($) investment	Dec. 31, 2022 USD ($) investment	Dec. 31, 2021 USD ($) investment	Dec. 31, 2020 USD ($)
Debt and Equity Securities, FV-NI [Line Items]
Number of securities in an unrealized loss position \| investment	1,030	1,030	1,233
Debt securities, available-for-sale, unrealized loss position	$ 21,434.8	$ 21,434.8	$ 18,697.7
Debt securities, available-for-sale, unrealized loss position, accumulated loss	1,049.2	1,049.2	248.6
Debt securities, available-for-sale, accumulated gross unrealized loss	1,067.8	1,067.8	248.6
Available for sale, amortized cost	27,760.0	27,760.0	37,948.5
Available for sale	26,699.9	26,699.9	38,010.5
Debt securities, available-for-sale, realized loss	(213.0)	214.0	1.7	$ 3.8
Allowance for credit losses, available-for-sale securities	567.2	567.2	531.9
Debt securities, held-to-maturity, amortized cost	25,036.1	25,036.1	23,564.5
Debt securities, held-to-maturity, accumulated unrecognized Loss	$ 2,158.2	$ 2,158.2	283.6
Transferred from available for sale to held to maturity			$ 6,900.0
Percentage of debt securities, held-to-maturity, portfolio	1	1	1
Gross proceeds from sale of securities			$ 116.7	$ 879.9
Draw period for credit line products		10 years
Moodys And Standard Poors A Or Higher Rating
Debt and Equity Securities, FV-NI [Line Items]
Percentage of debt securities, held-to-maturity, portfolio	0.97	0.97	0.94
Moodys And Standard Poors Not Rated
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, held-to-maturity, amortized cost	$ 502.7	$ 502.7	$ 1,191.0
Percentage of debt securities, held-to-maturity, portfolio	0.02	0.02	0.05
Government Sponsored Agency
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, available-for-sale, unrealized loss position	$ 10,369.1	$ 10,369.1	$ 10,028.7
Debt securities, available-for-sale, unrealized loss position, accumulated loss	351.6	351.6	110.2
Debt securities, available-for-sale, accumulated gross unrealized loss	351.6	351.6	110.2
Available for sale, amortized cost	11,892.5	11,892.5	18,092.1
Available for sale	11,545.2	11,545.2	18,075.6
Debt securities, held-to-maturity, amortized cost	9,407.7	9,407.7	5,927.6
Debt securities, held-to-maturity, accumulated unrecognized Loss	1,076.0	1,076.0	106.1
Government Sponsored Agency \| Moodys And Standard Poors Not Rated
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, held-to-maturity, amortized cost	0.0	0.0	0.0
Corporate Debt
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, available-for-sale, unrealized loss position	557.6	557.6	693.7
Debt securities, available-for-sale, unrealized loss position, accumulated loss	17.4	17.4	9.7
Debt securities, available-for-sale, accumulated gross unrealized loss	26.9	26.9	9.7
Available for sale, amortized cost	1,774.3	1,774.3	2,319.8
Available for sale	1,747.6	1,747.6	2,341.7
Debt securities, held-to-maturity, amortized cost	713.3	713.3	901.8
Debt securities, held-to-maturity, accumulated unrecognized Loss	45.4	45.4	6.5
Gross proceeds from sale of securities		138.7
Corporate Debt \| Moodys And Standard Poors Not Rated
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, held-to-maturity, amortized cost	0.0	0.0	0.0
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, available-for-sale, unrealized loss position	2,112.5	2,112.5	1,289.1
Debt securities, available-for-sale, unrealized loss position, accumulated loss	157.6	157.6	35.4
Debt securities, available-for-sale, accumulated gross unrealized loss	166.7	166.7	35.4
Available for sale, amortized cost	2,645.8	2,645.8	3,052.4
Available for sale	2,479.4	2,479.4	3,045.1
Debt securities, held-to-maturity, amortized cost	5,703.3	5,703.3	6,098.0
Debt securities, held-to-maturity, accumulated unrecognized Loss	436.1	436.1	80.0
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds \| Moodys And Standard Poors Not Rated
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, held-to-maturity, amortized cost	0.0	0.0	0.0
Covered Bonds
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, available-for-sale, unrealized loss position	280.8	280.8	92.1
Debt securities, available-for-sale, unrealized loss position, accumulated loss	14.7	14.7	0.9
Debt securities, available-for-sale, accumulated gross unrealized loss	14.7	14.7	0.9
Available for sale, amortized cost	403.1	403.1	502.6
Available for sale	388.7	388.7	505.6
Debt securities, held-to-maturity, amortized cost	2,530.3	2,530.3	2,942.4
Debt securities, held-to-maturity, accumulated unrecognized Loss	158.7	158.7	9.6
Covered Bonds \| Moodys And Standard Poors Not Rated
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, held-to-maturity, amortized cost	0.0	0.0	$ 0.0
Available For Sale, Debt Securities, Portfolio For Sale
Debt and Equity Securities, FV-NI [Line Items]
Available for sale, amortized cost	2,300.0	2,300.0
Available for sale	$ 2,100.0	$ 2,100.0

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