Fair Value Measurements - Carrying Amount and Estimated Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Assets
Investment securities available-for-sale	$ 2,348	$ 2,116
Investment securities held-to-maturity	516	599
Loans held-for-sale	5,598	5,219
Loans held-for-investment	12	12
Mortgage servicing rights	261	291
Carrying Value
Assets
Cash and cash equivalents	227	426
Investment securities available-for-sale	2,348	2,116
Investment securities held-to-maturity	496	598
Loans held-for-sale	5,615	5,258
Loans held-for-investment	14,808	12,129
Loans with government guarantees	1,791	736
Mortgage servicing rights	261	291
Federal Home Loan Bank stock	377	303
Bank owned life insurance	353	349
Repossessed assets	7	10
Other assets, foreclosure claims	30	45
Derivative financial instruments, assets	281	62
Liabilities
Federal Home Loan Bank advances	(4,554)	(4,815)
Long-term debt	(493)	(496)
DOJ Liability	(35)	(35)
Contingent consideration	(27)	(10)
Derivative financial instruments, liabilities	(68)	(18)
Carrying Value | Demand deposits and savings accounts
Liabilities
Deposits	(7,943)	(6,811)
Carrying Value | Certificates of deposit
Liabilities
Deposits	(1,826)	(2,353)
Carrying Value | Wholesale deposits
Liabilities
Deposits	(867)	(633)
Carrying Value | Government deposits
Liabilities
Deposits	(1,193)	(1,213)
Carrying Value | Custodial deposits
Liabilities
Deposits	(6,068)	(4,136)
Estimated Fair Value
Assets
Cash and cash equivalents	227	426
Investment securities available-for-sale	2,348	2,116
Investment securities held-to-maturity	516	599
Loans held-for-sale	5,615	5,258
Loans held-for-investment	14,757	12,031
Loans with government guarantees	1,739	707
Mortgage servicing rights	261	291
Federal Home Loan Bank stock	377	303
Bank owned life insurance	353	349
Repossessed assets	7	10
Other assets, foreclosure claims	30	45
Derivative financial instruments, assets	281	88
Liabilities
Federal Home Loan Bank advances	(4,586)	(4,816)
Long-term debt	(454)	(462)
DOJ Liability	(35)	(35)
Contingent consideration	(27)	(10)
Derivative financial instruments, liabilities	(68)	(44)
Estimated Fair Value | Demand deposits and savings accounts
Liabilities
Deposits	(7,445)	(6,050)
Estimated Fair Value | Certificates of deposit
Liabilities
Deposits	(1,847)	(2,368)
Estimated Fair Value | Wholesale deposits
Liabilities
Deposits	(889)	(640)
Estimated Fair Value | Government deposits
Liabilities
Deposits	(1,170)	(1,156)
Estimated Fair Value | Custodial deposits
Liabilities
Deposits	(6,050)	(4,066)
Estimated Fair Value | Level 1
Assets
Cash and cash equivalents	227	426
Investment securities available-for-sale	0	0
Investment securities held-to-maturity	0	0
Loans held-for-sale	0	0
Loans held-for-investment	0	0
Loans with government guarantees	0	0
Mortgage servicing rights	0	0
Federal Home Loan Bank stock	0	0
Bank owned life insurance	0	0
Repossessed assets	0	0
Other assets, foreclosure claims	0	0
Derivative financial instruments, assets	0	0
Liabilities
Federal Home Loan Bank advances	0	0
Long-term debt	0	0
DOJ Liability	0	0
Contingent consideration	0	0
Derivative financial instruments, liabilities	0	0
Estimated Fair Value | Level 1 | Demand deposits and savings accounts
Liabilities
Deposits	0	0
Estimated Fair Value | Level 1 | Certificates of deposit
Liabilities
Deposits	0	0
Estimated Fair Value | Level 1 | Wholesale deposits
Liabilities
Deposits	0	0
Estimated Fair Value | Level 1 | Government deposits
Liabilities
Deposits	0	0
Estimated Fair Value | Level 1 | Custodial deposits
Liabilities
Deposits	0	0
Estimated Fair Value | Level 2
Assets
Cash and cash equivalents	0	0
Investment securities available-for-sale	2,348	2,116
Investment securities held-to-maturity	516	599
Loans held-for-sale	5,615	5,258
Loans held-for-investment	10	10
Loans with government guarantees	1,739	707
Mortgage servicing rights	0	0
Federal Home Loan Bank stock	377	303
Bank owned life insurance	353	349
Repossessed assets	0	0
Other assets, foreclosure claims	30	45
Derivative financial instruments, assets	76	54
Liabilities
Federal Home Loan Bank advances	(4,586)	(4,816)
Long-term debt	(454)	(462)
DOJ Liability	0	0
Contingent consideration	0	0
Derivative financial instruments, liabilities	(68)	(43)
Estimated Fair Value | Level 2 | Demand deposits and savings accounts
Liabilities
Deposits	(7,445)	(6,050)
Estimated Fair Value | Level 2 | Certificates of deposit
Liabilities
Deposits	(1,847)	(2,368)
Estimated Fair Value | Level 2 | Wholesale deposits
Liabilities
Deposits	(889)	(640)
Estimated Fair Value | Level 2 | Government deposits
Liabilities
Deposits	(1,170)	(1,156)
Estimated Fair Value | Level 2 | Custodial deposits
Liabilities
Deposits	(6,050)	(4,066)
Estimated Fair Value | Level 3
Assets
Cash and cash equivalents	0	0
Investment securities available-for-sale	0	0
Investment securities held-to-maturity	0	0
Loans held-for-sale	0	0
Loans held-for-investment	14,747	12,021
Loans with government guarantees	0	0
Mortgage servicing rights	261	291
Federal Home Loan Bank stock	0	0
Bank owned life insurance	0	0
Repossessed assets	7	10
Other assets, foreclosure claims	0	0
Derivative financial instruments, assets	205	34
Liabilities
Federal Home Loan Bank advances	0	0
Long-term debt	0	0
DOJ Liability	(35)	(35)
Contingent consideration	(27)	(10)
Derivative financial instruments, liabilities	0	(1)
Estimated Fair Value | Level 3 | Demand deposits and savings accounts
Liabilities
Deposits	0	0
Estimated Fair Value | Level 3 | Certificates of deposit
Liabilities
Deposits	0	0
Estimated Fair Value | Level 3 | Wholesale deposits
Liabilities
Deposits	0	0
Estimated Fair Value | Level 3 | Government deposits
Liabilities
Deposits	0	0
Estimated Fair Value | Level 3 | Custodial deposits
Liabilities
Deposits	$ 0	$ 0