Investment Securities - Credit Quality Indicators (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	$ 3,453.7	$ 1,687.6
AAA Rating
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	3,260.7	1,626.2
AA Rating
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	92.8	31.6
A Rating
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	11.5	18.7
BBB Rating
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	65.1	7.0
BB Rating
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	10.0
Not Rated
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	13.6	4.1
US Treasury Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	396.6
US Treasury Securities [Member] | AAA Rating
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	396.6
US Treasury Securities [Member] | AA Rating
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	0.0
US Treasury Securities [Member] | A Rating
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	0.0
US Treasury Securities [Member] | BBB Rating
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	0.0
US Treasury Securities [Member] | BB Rating
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	0.0
US Treasury Securities [Member] | Not Rated
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	0.0
State, county and municipal securities
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	181.2	67.6
State, county and municipal securities | AAA Rating
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	68.3	17.2
State, county and municipal securities | AA Rating
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	92.8	31.6
State, county and municipal securities | A Rating
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	11.5	14.7
State, county and municipal securities | BBB Rating
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	0.0	0.0
State, county and municipal securities | BB Rating
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	0.0
State, county and municipal securities | Not Rated
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	8.6	4.1
US Government Agencies Debt Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	351.7
US Government Agencies Debt Securities [Member] | AAA Rating
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	351.7
US Government Agencies Debt Securities [Member] | AA Rating
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	0.0
US Government Agencies Debt Securities [Member] | A Rating
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	0.0
US Government Agencies Debt Securities [Member] | BBB Rating
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	0.0
US Government Agencies Debt Securities [Member] | BB Rating
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	0.0
US Government Agencies Debt Securities [Member] | Not Rated
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	0.0
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	2,444.1	1,609.0
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | FNMA and FHLMC
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	2,233.6	1,439.1
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | GNMA
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	210.5	169.9
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | AAA Rating | FNMA and FHLMC
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	2,233.6	1,439.1
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | AAA Rating | GNMA
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	210.5	169.9
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | AA Rating | FNMA and FHLMC
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	0.0	0.0
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | AA Rating | GNMA
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	0.0	0.0
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | A Rating | FNMA and FHLMC
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	0.0	0.0
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | A Rating | GNMA
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	0.0	0.0
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | BBB Rating | FNMA and FHLMC
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	0.0	0.0
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | BBB Rating | GNMA
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	0.0	0.0
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | BB Rating | FNMA and FHLMC
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	0.0
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | BB Rating | GNMA
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	0.0
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | Not Rated | FNMA and FHLMC
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	0.0	0.0
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | Not Rated | GNMA
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	0.0	0.0
Corporate Debt Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	80.1	11.0
Corporate Debt Securities [Member] | AAA Rating
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	0.0	0.0
Corporate Debt Securities [Member] | AA Rating
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	0.0	0.0
Corporate Debt Securities [Member] | A Rating
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	0.0	4.0
Corporate Debt Securities [Member] | BBB Rating
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	65.1	7.0
Corporate Debt Securities [Member] | BB Rating
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	10.0
Corporate Debt Securities [Member] | Not Rated
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	$ 5.0	$ 0.0