Securities (Narrative) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2022 USD ($) investment	Sep. 30, 2021 USD ($)	Sep. 30, 2022 USD ($) investment	Sep. 30, 2021 USD ($)	Dec. 31, 2021 USD ($) investment
Debt and Equity Securities, FV-NI [Line Items]
Number of securities in an unrealized loss position | investment	1,153		1,153		1,233
Debt securities, unrealized losses	$ 1,284,100,000		$ 1,284,100,000		$ 248,600,000
Provision for credit losses	(1,400,000)	$ 13,000,000.0	(6,200,000)	$ 70,000,000.0
Net amount of recognized liabilities for repurchase agreements	561,400,000		561,400,000		531,900,000
Held to maturity securities	25,249,800,000		25,249,800,000		23,564,500,000
Debt securities, held-to-maturity, accumulated unrecognized loss	2,186,300,000		2,186,300,000		$ 283,600,000
Held to maturity securities, transferred from available for sale	$ 6,600,000,000	0	$ 6,600,000,000	6,900,000,000
Percentage of debt securities, held-to-maturity, portfolio	1		1		1
Debt securities, gain (loss)	$ (300,000)	100,000	$ (300,000)	100,000
Moodys And Standard Poors A Or Higher Rating
Debt and Equity Securities, FV-NI [Line Items]
Percentage of debt securities, held-to-maturity, portfolio	0.95		0.95		0.94
BBB
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities	$ 296,900,000		$ 296,900,000		$ 345,000,000.0
Percentage of debt securities, held-to-maturity, portfolio	0.01		0.01		0.01
NOT RATED
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities	$ 918,700,000		$ 918,700,000		$ 1,191,000,000
Percentage of debt securities, held-to-maturity, portfolio	0.04		0.04		0.05
Government Sponsored Agency
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, unrealized losses	$ 299,900,000		$ 299,900,000		$ 110,200,000
Held to maturity securities	9,627,100,000		9,627,100,000		5,927,600,000
Debt securities, held-to-maturity, accumulated unrecognized loss	1,049,200,000		1,049,200,000		106,100,000
Government Sponsored Agency | BBB
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities	0		0		0
Government Sponsored Agency | NOT RATED
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities	0		0		0
Obligations of States and Political Subdivisions
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, unrealized losses	125,500,000		125,500,000		38,600,000
Held to maturity securities	2,558,500,000		2,558,500,000		800,000
Debt securities, held-to-maturity, accumulated unrecognized loss	133,500,000		133,500,000		0
Obligations of States and Political Subdivisions | BBB
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities	0		0		0
Obligations of States and Political Subdivisions | NOT RATED
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities	0		0		0
Corporate Debt
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, unrealized losses	$ 88,100,000		$ 88,100,000		$ 9,700,000
Percent of corporate debt portfolio	12.00%		12.00%		14.00%
Provision for credit losses	$ 900,000	$ 0	$ (800,000)	$ 0
Net amount of recognized liabilities for repurchase agreements	800,000		800,000		$ 0
Held to maturity securities	798,200,000		798,200,000		901,800,000
Debt securities, held-to-maturity, accumulated unrecognized loss	48,600,000		48,600,000		6,500,000
Corporate Debt | BBB
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities	0		0		0
Corporate Debt | NOT RATED
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities	0		0		0
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, unrealized losses	174,100,000		174,100,000		35,400,000
Held to maturity securities	5,621,800,000		5,621,800,000		6,098,000,000
Debt securities, held-to-maturity, accumulated unrecognized loss	491,400,000		491,400,000		80,000,000
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds | BBB
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities	1,000,000.0		1,000,000.0		1,100,000
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds | NOT RATED
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities	0		0		0
Non-U.S. Government
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, unrealized losses	28,600,000		28,600,000		9,500,000
Held to maturity securities	2,844,900,000		2,844,900,000		5,773,300,000
Debt securities, held-to-maturity, accumulated unrecognized loss	134,300,000		134,300,000		9,800,000
Non-U.S. Government | BBB
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities	295,900,000		295,900,000		343,900,000
Non-U.S. Government | NOT RATED
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities	$ 0		$ 0		$ 0