Securities (Narrative) (Details)	12 Months Ended
	Dec. 31, 2021 USD ($) investment	Dec. 31, 2020 USD ($) investment	Dec. 31, 2019 USD ($)
Debt and Equity Securities, FV-NI [Line Items]
Number of securities in an unrealized loss position | investment	1,233	412
Debt securities, available-for-sale, unrealized loss position	$ 18,697,700,000	$ 6,366,600,000
Debt securities, available-for-sale, unrealized loss position, accumulated loss	248,600,000	31,300,000
Debt securities, available-for-sale, accumulated gross unrealized loss	248,600,000	31,300,000
Provision for credit losses	(81,500,000)	125,000,000	$ (14,500,000)
Allowance for credit losses, available-for-sale securities	531,900,000	39,800,000
Debt securities, held-to-maturity, amortized cost	23,564,500,000	17,791,100,000
Debt securities, held-to-maturity, accumulated unrecognized Loss	283,600,000	78,000,000.0
Transferred from available for sale to held to maturity	$ 6,900,000,000	$ 301,500,000
Percentage of debt securities, held-to-maturity, portfolio	1	1
Gross proceeds from sale of securities	$ 116,700,000	$ 879,900,000	$ 1,200,000,000
Moodys And Standard Poors A Or Higher Rating
Debt and Equity Securities, FV-NI [Line Items]
Percentage of debt securities, held-to-maturity, portfolio	0.94	0.93
Moodys And Standard Poors Not Rated
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, held-to-maturity, amortized cost	$ 1,191,000,000	$ 1,261,800,000
Percentage of debt securities, held-to-maturity, portfolio	0.05	0.07
Government Sponsored Agency
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, available-for-sale, unrealized loss position	$ 10,028,700,000	$ 4,931,000,000
Debt securities, available-for-sale, unrealized loss position, accumulated loss	110,200,000	26,900,000
Debt securities, available-for-sale, accumulated gross unrealized loss	110,200,000	26,900,000
Debt securities, held-to-maturity, amortized cost	5,927,600,000	3,000,000.0
Debt securities, held-to-maturity, accumulated unrecognized Loss	106,100,000	0
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
Corporate Debt
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, available-for-sale, unrealized loss position	693,700,000	66,600,000
Debt securities, available-for-sale, unrealized loss position, accumulated loss	9,700,000	100,000
Debt securities, available-for-sale, accumulated gross unrealized loss	$ 9,700,000	$ 100,000
Percent of corporate debt portfolio	14.00%	16.00%
Provision for credit losses	$ 0	$ 0
Allowance for credit losses, available-for-sale securities	0	0
Debt securities, held-to-maturity, amortized cost	901,800,000	588,000,000.0
Debt securities, held-to-maturity, accumulated unrecognized Loss	6,500,000	100,000
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
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	1,289,100,000	212,700,000
Debt securities, available-for-sale, unrealized loss position, accumulated loss	35,400,000	600,000
Debt securities, available-for-sale, accumulated gross unrealized loss	35,400,000	600,000
Debt securities, held-to-maturity, amortized cost	6,098,000,000	3,648,000,000
Debt securities, held-to-maturity, accumulated unrecognized Loss	80,000,000	900,000
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
Other securities
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, held-to-maturity, amortized cost	516,300,000	454,600,000
Debt securities, held-to-maturity, accumulated unrecognized Loss	71,600,000	76,500,000
Other securities | Moodys And Standard Poors Not Rated
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, held-to-maturity, amortized cost	$ 516,300,000	$ 454,600,000