Investment Securities - Narrative (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2023 USD ($) Investments	Jun. 30, 2022 USD ($)	Jun. 30, 2023 USD ($) Investments	Jun. 30, 2022 USD ($)	Mar. 31, 2023 USD ($)	Dec. 31, 2022 USD ($) Investments	Mar. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Schedule of Held-to-maturity Securities [Line Items]
Allowance for Credit Losses						$ 0
Debt Securities, Held-to-maturity, Allowance for Credit Loss	$ 700,000	$ 1,600,000	$ 700,000	$ 1,600,000	$ 700,000	1,900,000	$ 1,600,000	$ 0
Interest Receivable	119,100,000		119,100,000			118,300,000
Debt Securities, Available-for-sale, Realized Gain	0	0		0
Debt Securities, Available-for-sale, Realized Loss	0	$ 0	(23,500,000)	$ 0
Securities Sold under Agreements to Repurchase, Fair Value of Collateral	7,227,800,000		7,227,800,000			4,998,900,000
Securities Loaned or Sold under Agreements to Repurchase, Fair Value Disclosure	$ 6,455,100,000		$ 6,455,100,000			$ 4,432,000,000
Investment securities in an unrealized loss position (securities) | Investments	1,030		1,030			1,222
Debt Securities, Current	$ 853,000,000		$ 853,000,000
Callable Within One Year
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost of investment securities callable after one year but within five years	1,593,800,000		1,593,800,000
Fair value of investment securities callable after one year but within five years	1,521,200,000		1,521,200,000
Callable structured notes amortized costs	$ 0		$ 0