Investment Securities - Gross Unrealized Losses and Fair Values of Investment Securities (Details)	12 Months Ended
Dec. 31, 2019 USD ($)	Dec. 31, 2021 USD ($) Investments	Dec. 31, 2020 USD ($) Investments
Investments, Debt and Equity Securities [Abstract]
Debt Securities, Held-to-maturity		$ 1,687,600,000	$ 51,600,000
Available-for-Sale and Held-to-Maturity:
Investment securities in an unrealized loss position (number of securities) \| Investments		285	181
Less than 12 Months		$ 1,067,700,000
Less than 12 Months		(35,700,000)
12 Months or More		0
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		0
Debt Securities, Held-to-maturity, Unrealized Loss Position, Fair Value		1,067,700,000
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss		(35,700,000)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months		2,760,300,000	$ 838,600,000
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer		68,700,000	16,600,000
Debt Securities, Available-for-sale, Unrealized Loss Position		2,829,000,000	855,200,000
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss		(59,400,000)	(5,700,000)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		(58,300,000)	(5,500,000)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		(1,100,000)	(200,000)
Other than Temporary Impairment Losses, Investments	$ 0
Related Allowance		0
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Investments, Debt and Equity Securities [Abstract]
Debt Securities, Held-to-maturity		1,609,000,000	1,000,000.0
Available-for-Sale and Held-to-Maturity:
Less than 12 Months		1,038,700,000
Less than 12 Months		(35,300,000)
12 Months or More		0
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		0
Debt Securities, Held-to-maturity, Unrealized Loss Position, Fair Value		1,038,700,000
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss		(35,300,000)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months		1,262,800,000	434,000,000.0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer		26,400,000	12,300,000
Debt Securities, Available-for-sale, Unrealized Loss Position		1,289,200,000	446,300,000
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss		(23,300,000)	(2,500,000)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		(23,000,000.0)	(2,400,000)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		(300,000)	(100,000)
US Government Agencies Debt Securities [Member]
Available-for-Sale and Held-to-Maturity:
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months		297,000,000.0	235,600,000
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer		16,400,000	0
Debt Securities, Available-for-sale, Unrealized Loss Position		313,400,000	235,600,000
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss		(9,200,000)	(2,000,000.0)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		(8,900,000)	(2,000,000.0)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		(300,000)	0
Corporate Debt Securities [Member]
Investments, Debt and Equity Securities [Abstract]
Debt Securities, Held-to-maturity		11,000,000.0	3,900,000
Available-for-Sale and Held-to-Maturity:
Less than 12 Months		29,000,000.0
Less than 12 Months		(400,000)
12 Months or More		0
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		0
Debt Securities, Held-to-maturity, Unrealized Loss Position, Fair Value		29,000,000.0
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss		(400,000)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months		109,900,000	20,900,000
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer		20,900,000	0
Debt Securities, Available-for-sale, Unrealized Loss Position		130,800,000	20,900,000
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss		(3,600,000)	(100,000)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		(3,300,000)	(100,000)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		(300,000)	0
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Available-for-Sale and Held-to-Maturity:
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months		127,200,000	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer		0	4,300,000
Debt Securities, Available-for-sale, Unrealized Loss Position		127,200,000	4,300,000
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss		(1,100,000)	(100,000)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		(1,100,000)	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		0	(100,000)
US Treasury notes
Available-for-Sale and Held-to-Maturity:
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months		684,700,000
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer		0
Debt Securities, Available-for-sale, Unrealized Loss Position		684,700,000
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss		(12,900,000)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		(12,900,000)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		0
State, county and municipal securities
Investments, Debt and Equity Securities [Abstract]
Debt Securities, Held-to-maturity		67,600,000	46,600,000
Available-for-Sale and Held-to-Maturity:
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months		278,700,000	148,100,000
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer		5,000,000.0	0
Debt Securities, Available-for-sale, Unrealized Loss Position		283,700,000	148,100,000
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss		(9,300,000)	(1,000,000.0)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		(9,100,000)	(1,000,000.0)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		$ (200,000)	$ 0

Available-for-Sale and Held-to-Maturity, Securities in Unrealized Loss Positions [Abstract]

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Available-for-Sale and Held-to-Maturity, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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