Fair Value Measurements - Carrying Amount and Estimated Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021
Assets
Investment securities available-for-sale	$ 2,627.0	$ 1,804.0
Investment securities held-to-maturity	145.0	209.0
Loans held-for-sale	1,822.0	4,920.0
Loans held-for-investment	24.0	16.0
Mortgage servicing rights	1,026.0	392.0
Carrying Value
Assets
Cash and cash equivalents	418.0	1,051.0
Investment securities available-for-sale	2,627.0	1,804.0
Investment securities held-to-maturity	159.0	205.0
Loans held-for-sale	1,830.0	5,054.0
Loans held-for-investment	15,793.0	13,408.0
Loans with government guarantees	1,370.0	1,650.0
Mortgage servicing rights	1,026.0	392.0
Federal Home Loan Bank stock	329.0	377.0
Bank owned life insurance	372.0	365.0
Repossessed assets	6.0	6.0
Other assets, foreclosure claims	13.0	7.0
Derivative financial instruments, assets	354.0	141.0
Liabilities
Federal Home Loan Bank advances	(4,450.0)	(3,280.0)
Long-term debt	(390.0)	(396.0)
Derivative financial instruments, liabilities	(122.0)	(20.0)
Carrying Value | Demand deposits and savings accounts
Liabilities
Deposits	(8,697.0)	(9,313.0)
Carrying Value | Certificates of deposit
Liabilities
Deposits	(851.0)	(951.0)
Carrying Value | Wholesale deposits
Liabilities
Deposits	(836.0)	(1,141.0)
Carrying Value | Government deposits
Liabilities
Deposits	(1,851.0)	(2,000.0)
Carrying Value | Company controlled deposits
Liabilities
Deposits	(4,356.0)	(4,604.0)
Estimated Fair Value
Assets
Cash and cash equivalents	418.0	1,051.0
Investment securities available-for-sale	2,627.0	1,804.0
Investment securities held-to-maturity	145.0	209.0
Loans held-for-sale	1,830.0	5,054.0
Loans held-for-investment	15,364.0	13,453.0
Loans with government guarantees	1,370.0	1,650.0
Mortgage servicing rights	1,026.0	392.0
Federal Home Loan Bank stock	329.0	377.0
Bank owned life insurance	372.0	365.0
Repossessed assets	6.0	6.0
Other assets, foreclosure claims	13.0	7.0
Derivative financial instruments, assets	354.0	141.0
Liabilities
Federal Home Loan Bank advances	(4,441.0)	(3,288.0)
Long-term debt	(333.0)	(340.0)
Derivative financial instruments, liabilities	(122.0)	(20.0)
Estimated Fair Value | Demand deposits and savings accounts
Liabilities
Deposits	(7,132.0)	(8,469.0)
Estimated Fair Value | Certificates of deposit
Liabilities
Deposits	(838.0)	(952.0)
Estimated Fair Value | Wholesale deposits
Liabilities
Deposits	(800.0)	(1,137.0)
Estimated Fair Value | Government deposits
Liabilities
Deposits	(1,605.0)	(1,904.0)
Estimated Fair Value | Company controlled deposits
Liabilities
Deposits	(4,237.0)	(4,580.0)
Estimated Fair Value | Level 1
Assets
Cash and cash equivalents	418.0	1,051.0
Investment securities available-for-sale	0.0	0.0
Investment securities held-to-maturity	0.0	0.0
Loans held-for-sale	0.0	0.0
Loans held-for-investment	0.0	0.0
Loans with government guarantees	0.0	0.0
Mortgage servicing rights	0.0	0.0
Federal Home Loan Bank stock	0.0	0.0
Bank owned life insurance	0.0	0.0
Repossessed assets	0.0	0.0
Other assets, foreclosure claims	0.0	0.0
Derivative financial instruments, assets	0.0	0.0
Liabilities
Federal Home Loan Bank advances	0.0	0.0
Long-term debt	0.0	0.0
Derivative financial instruments, liabilities	0.0	0.0
Estimated Fair Value | Level 1 | Demand deposits and savings accounts
Liabilities
Deposits	0.0	0.0
Estimated Fair Value | Level 1 | Certificates of deposit
Liabilities
Deposits	0.0	0.0
Estimated Fair Value | Level 1 | Wholesale deposits
Liabilities
Deposits	0.0	0.0
Estimated Fair Value | Level 1 | Government deposits
Liabilities
Deposits	0.0	0.0
Estimated Fair Value | Level 1 | Company controlled deposits
Liabilities
Deposits	0.0	0.0
Estimated Fair Value | Level 2
Assets
Cash and cash equivalents	0.0	0.0
Investment securities available-for-sale	2,627.0	1,804.0
Investment securities held-to-maturity	145.0	209.0
Loans held-for-sale	1,830.0	5,054.0
Loans held-for-investment	23.0	14.0
Loans with government guarantees	1,370.0	1,650.0
Mortgage servicing rights	0.0	0.0
Federal Home Loan Bank stock	329.0	377.0
Bank owned life insurance	372.0	365.0
Repossessed assets	0.0	0.0
Other assets, foreclosure claims	13.0	7.0
Derivative financial instruments, assets	344.0	87.0
Liabilities
Federal Home Loan Bank advances	(4,441.0)	(3,288.0)
Long-term debt	(333.0)	(340.0)
Derivative financial instruments, liabilities	(93.0)	(19.0)
Estimated Fair Value | Level 2 | Demand deposits and savings accounts
Liabilities
Deposits	(7,132.0)	(8,469.0)
Estimated Fair Value | Level 2 | Certificates of deposit
Liabilities
Deposits	(838.0)	(952.0)
Estimated Fair Value | Level 2 | Wholesale deposits
Liabilities
Deposits	(800.0)	(1,137.0)
Estimated Fair Value | Level 2 | Government deposits
Liabilities
Deposits	(1,605.0)	(1,904.0)
Estimated Fair Value | Level 2 | Company controlled deposits
Liabilities
Deposits	(4,237.0)	(4,580.0)
Estimated Fair Value | Level 3
Assets
Cash and cash equivalents	0.0	0.0
Investment securities available-for-sale	0.0	0.0
Investment securities held-to-maturity	0.0	0.0
Loans held-for-sale	0.0	0.0
Loans held-for-investment	15,341.0	13,439.0
Loans with government guarantees	0.0	0.0
Mortgage servicing rights	1,026.0	392.0
Federal Home Loan Bank stock	0.0	0.0
Bank owned life insurance	0.0	0.0
Repossessed assets	6.0	6.0
Other assets, foreclosure claims	0.0	0.0
Derivative financial instruments, assets	10.0	54.0
Liabilities
Federal Home Loan Bank advances	0.0	0.0
Long-term debt	0.0	0.0
Derivative financial instruments, liabilities	(29.0)	(1.0)
Estimated Fair Value | Level 3 | Demand deposits and savings accounts
Liabilities
Deposits	0.0	0.0
Estimated Fair Value | Level 3 | Certificates of deposit
Liabilities
Deposits	0.0	0.0
Estimated Fair Value | Level 3 | Wholesale deposits
Liabilities
Deposits	0.0	0.0
Estimated Fair Value | Level 3 | Government deposits
Liabilities
Deposits	0.0	0.0
Estimated Fair Value | Level 3 | Company controlled deposits
Liabilities
Deposits	$ 0.0	$ 0.0