Borrowings - Schedule of Long-term Borrowings (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2022	Dec. 31, 2021
Debt Instrument [Line Items]
Capital lease obligations	$ 8	$ 4
Unamortized issuance costs	(2)	(2)
Unamortized purchase accounting adjustment	94	(2)
Total long-term borrowings	5,215	1,195
Subordinated Debt
Debt Instrument [Line Items]
Unamortized purchase accounting adjustment	(72)	(2)
Fixed-to-Floating subordinated notes at 3.375% | Subordinated Debt
Debt Instrument [Line Items]
Long-term debt, gross	$ 350
Debt instrument, stated interest rate	3.375%
Fixed subordinated notes at 6.125% | Subordinated Debt
Debt Instrument [Line Items]
Long-term debt, gross	$ 400
Debt instrument, stated interest rate	6.125%
Fixed-to-Fixed subordinated notes at 4.125% | Subordinated Debt
Debt Instrument [Line Items]
Long-term debt, gross	$ 100
Debt instrument, stated interest rate	4.125%
5.00% Senior Unsecured Notes Due 2022 | Senior Notes
Debt Instrument [Line Items]
Debt instrument, stated interest rate	5.00%
5.00% Senior Unsecured Notes Due 2023 | Senior Notes
Debt Instrument [Line Items]
Debt instrument, stated interest rate	5.00%
4.750% Senior Unsecured Notes Due 2024 | Senior Notes
Debt Instrument [Line Items]
Debt instrument, stated interest rate	4.75%
5.250% Senior Unsecured Notes Due 2025 | Senior Notes
Debt Instrument [Line Items]
Debt instrument, stated interest rate	5.25%
Parent | Unsecured term loan at 1-month LIBOR plus 1.10% | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 0	68
Parent | Unsecured term loan at 1-month LIBOR plus 1.10% | Senior Notes | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate	1.10%
Parent | Fixed-to-Floating subordinated notes at 3.375% | Subordinated Debt
Debt Instrument [Line Items]
Long-term debt, gross	$ 350	350
Debt instrument, stated interest rate	3.375%
Parent | Junior subordinated debenture at 3-month LIBOR plus 2.25% (FCB/SC Capital Trust II) | Subordinated Debt
Debt Instrument [Line Items]
Long-term debt, gross	$ 20	20
Parent | Junior subordinated debenture at 3-month LIBOR plus 2.25% (FCB/SC Capital Trust II) | Subordinated Debt | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate	2.25%
Parent | Junior subordinated debenture at 3-month LIBOR plus 1.75% (FCB/NC Capital Trust III) | Subordinated Debt
Debt Instrument [Line Items]
Long-term debt, gross	$ 88	88
Parent | Junior subordinated debenture at 3-month LIBOR plus 1.75% (FCB/NC Capital Trust III) | Subordinated Debt | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate	1.75%
Subsidiaries | Senior unsecured fixed to floating rate notes at 3.929% | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 500	0
Debt instrument, stated interest rate	3.929%
Subsidiaries | Senior unsecured fixed to floating rate notes at 2.969% | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 315	0
Debt instrument, stated interest rate	2.969%
Subsidiaries | Fixed senior unsecured notes at 6.00% | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 51	0
Debt instrument, stated interest rate	6.00%
Subsidiaries | Fixed subordinated notes at 6.125% | Subordinated Debt
Debt Instrument [Line Items]
Long-term debt, gross	$ 400	0
Debt instrument, stated interest rate	6.125%
Subsidiaries | Fixed-to-Fixed subordinated notes at 4.125% | Subordinated Debt
Debt Instrument [Line Items]
Long-term debt, gross	$ 100	0
Debt instrument, stated interest rate	4.125%
Subsidiaries | Junior subordinated debentures at 3-month LIBOR plus 2.80% (Macon Capital Trust I) | Subordinated Debt
Debt Instrument [Line Items]
Long-term debt, gross	$ 14	14
Subsidiaries | Junior subordinated debentures at 3-month LIBOR plus 2.80% (Macon Capital Trust I) | Subordinated Debt | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate	2.80%
Subsidiaries | Junior subordinated debentures at 3-month LIBOR plus 2.85% (SCB Capital Trust I) | Subordinated Debt
Debt Instrument [Line Items]
Long-term debt, gross	$ 10	10
Subsidiaries | Junior subordinated debentures at 3-month LIBOR plus 2.85% (SCB Capital Trust I) | Subordinated Debt | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate	2.85%
Subsidiaries | Notes payable to FHLB of Atlanta at overnight SOFR plus spreads ranging from 0.24% to 0.37%. | Secured Debt
Debt Instrument [Line Items]
Long-term debt, gross	$ 3,250	0
Subsidiaries | Notes payable to FHLB of Atlanta at overnight SOFR plus spreads ranging from 0.24% to 0.37%. | Secured Debt | Secured Overnight Financing Rate (SOFR) | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate	0.24%
Subsidiaries | Notes payable to FHLB of Atlanta at overnight SOFR plus spreads ranging from 0.24% to 0.37%. | Secured Debt | Secured Overnight Financing Rate (SOFR) | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate	0.37%
Subsidiaries | Fixed notes payable to FHLB of Atlanta | Secured Debt
Debt Instrument [Line Items]
Long-term debt, gross	$ 0	645
Subsidiaries | Other secured financings | Secured Debt
Debt Instrument [Line Items]
Long-term debt, gross	$ 17	$ 0