Securities (Narrative) (Details)	1 Months Ended	3 Months Ended		12 Months Ended
	Jan. 31, 2023 USD ($)	Mar. 31, 2023 USD ($) investment	Mar. 31, 2022 USD ($)	Dec. 31, 2022 USD ($) investment
Debt and Equity Securities, FV-NI [Line Items]
Number of securities in an unrealized loss position | investment		1,013		1,030
Debt securities, unrealized losses		$ 807,000,000.0		$ 1,049,200,000
Debt securities, available-for-sale, realized loss				213,000,000
Available for Sale		24,627,500,000		26,699,900,000
Debt securities, available-for-sale, realized gain	$ 6,900,000
Provision for credit losses		14,500,000	$ 1,600,000
Held to maturity securities		24,716,200,000		25,036,100,000
Debt securities, held-to-maturity, accumulated unrecognized loss		$ 1,897,000,000		$ 2,158,200,000
Percentage of debt securities, held-to-maturity, portfolio		1		1
Debt securities, available-for-sale, realized gain (loss)		$ 6,900,000	0
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
BBB
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities		$ 329,000,000.0		$ 323,400,000
Percentage of debt securities, held-to-maturity, portfolio		0.01		0.01
NOT RATED
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities		$ 523,300,000		$ 502,700,000
Percentage of debt securities, held-to-maturity, portfolio		0.02		0.02
Government Sponsored Agency
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, unrealized losses		$ 258,500,000		$ 351,600,000
Available for Sale		11,433,400,000		11,545,200,000
Held to maturity securities		9,259,900,000		9,407,700,000
Debt securities, held-to-maturity, accumulated unrecognized loss		949,800,000		1,076,000,000
Government Sponsored Agency | BBB
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities		0		0
Government Sponsored Agency | NOT RATED
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities		0		0
Obligations of States and Political Subdivisions
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, unrealized losses		19,400,000		30,200,000
Available for Sale		291,900,000		787,600,000
Held to maturity securities		2,573,600,000		2,565,300,000
Debt securities, held-to-maturity, accumulated unrecognized loss		74,900,000		149,800,000
Debt securities, available-for-sale, realized gain (loss)		9,800,000
Obligations of States and Political Subdivisions | BBB
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities		0		0
Obligations of States and Political Subdivisions | NOT RATED
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities		0		0
Corporate Debt
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, unrealized losses		9,200,000		17,400,000
Available for Sale		634,500,000		1,747,600,000
Provision for credit losses		500,000	400,000
Net amount of recognized liabilities for repurchase agreements		1,800,000		1,300,000
Held to maturity securities		673,000,000.0		713,300,000
Debt securities, held-to-maturity, accumulated unrecognized loss		42,600,000		45,400,000
Proceeds from sale of investment securities		2,100,000,000	$ 0
Debt securities, available-for-sale, realized gain (loss)		(1,200,000)
Corporate Debt | BBB
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities		0		0
Corporate Debt | NOT RATED
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities		0		0
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, unrealized losses		106,400,000		157,600,000
Available for Sale		2,787,700,000		2,479,400,000
Held to maturity securities		5,700,300,000		5,703,300,000
Debt securities, held-to-maturity, accumulated unrecognized loss		397,100,000		436,100,000
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds | BBB
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities		1,100,000		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
Available For Sale, Debt Securities, Portfolio For Sale
Debt and Equity Securities, FV-NI [Line Items]
Available for Sale				2,100,000,000
Commercial Mortgage-Backed
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, unrealized losses		67,300,000		69,200,000
Available for Sale		903,900,000		1,387,800,000
Held to maturity securities		37,600,000
Debt securities, held-to-maturity, accumulated unrecognized loss		800,000
Debt securities, available-for-sale, realized gain (loss)		(900,000)
Commercial Mortgage-Backed | BBB
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities		0
Commercial Mortgage-Backed | NOT RATED
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities		0
Other Asset-Backed
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, unrealized losses		237,700,000		288,100,000
Available for Sale		5,010,400,000		5,256,200,000
Held to maturity securities		335,700,000		263,700,000
Debt securities, held-to-maturity, accumulated unrecognized loss		1,000,000.0		1,000,000.0
Debt securities, available-for-sale, realized gain (loss)		(800,000)
Other Asset-Backed | BBB
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities		0		0
Other Asset-Backed | NOT RATED
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities		$ 0		$ 0