Fair Value Measurements - Changes in Fair Value Included in Earnings (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Assets
Investment securities available-for-sale	$ 2,142	$ 2,142
Investment securities held-to-maturity	666	681
Loans held-for-sale	3,846	3,732
Loans held-for-investment	10	10
Mortgage servicing rights	278	290
Carrying Value
Assets
Cash and cash equivalents	390	408
Investment securities available-for-sale	2,142	2,142
Investment securities held-to-maturity	683	703
Loans held-for-sale	3,874	3,869
Loans held-for-investment	9,936	9,088
Loans with government guarantees	470	392
Mortgage servicing rights	278	290
Federal Home Loan Bank stock	303	303
Bank owned life insurance	342	340
Repossessed assets	8	7
Other assets, foreclosure claims	53	50
Derivative financial instruments, assets	57	57
Liabilities
Federal Home Loan Bank advances	(3,351)	(3,351)
Long-term debt	(495)	(495)
DOJ litigation settlement	(60)	(60)
Contingent consideration	(6)	(6)
Derivative financial instruments, liabilities	(46)	(46)
Carrying Value | Demand deposits and savings accounts
Liabilities
Deposits	(6,431)	(6,431)
Carrying Value | Certificates of deposit
Liabilities
Deposits	(2,584)	(2,584)
Carrying Value | Wholesale deposits
Liabilities
Deposits	(467)	(583)
Carrying Value | Government deposits
Liabilities
Deposits	(1,187)	(1,187)
Carrying Value | Custodial deposits
Liabilities
Deposits	(2,784)	(2,784)
Estimated Fair Value
Assets
Cash and cash equivalents	390	408
Investment securities available-for-sale	2,142	2,142
Investment securities held-to-maturity	666	681
Loans held-for-sale	3,874	3,870
Loans held-for-investment	10,093	8,966
Loans with government guarantees	451	374
Mortgage servicing rights	278	290
Federal Home Loan Bank stock	303	303
Bank owned life insurance	342	340
Repossessed assets	8	7
Other assets, foreclosure claims	53	50
Derivative financial instruments, assets	57	47
Liabilities
Federal Home Loan Bank advances	(3,343)	(3,383)
Long-term debt	(459)	(463)
DOJ litigation settlement	(60)	(60)
Contingent consideration	(6)	(6)
Derivative financial instruments, liabilities	(46)	(39)
Estimated Fair Value | Demand deposits and savings accounts
Liabilities
Deposits	(5,529)	(5,475)
Estimated Fair Value | Certificates of deposit
Liabilities
Deposits	(2,590)	(2,379)
Estimated Fair Value | Wholesale deposits
Liabilities
Deposits	(468)	(585)
Estimated Fair Value | Government deposits
Liabilities
Deposits	(1,116)	(1,145)
Estimated Fair Value | Custodial deposits
Liabilities
Deposits	(2,738)	(1,664)
Estimated Fair Value | Level 1
Assets
Cash and cash equivalents	390	408
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 litigation settlement	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	2,142	2,142
Investment securities held-to-maturity	666	681
Loans held-for-sale	3,874	3,870
Loans held-for-investment	8	8
Loans with government guarantees	451	374
Mortgage servicing rights	0	0
Federal Home Loan Bank stock	303	303
Bank owned life insurance	342	340
Repossessed assets	0	0
Other assets, foreclosure claims	53	50
Derivative financial instruments, assets	20	27
Liabilities
Federal Home Loan Bank advances	(3,343)	(3,383)
Long-term debt	(459)	(463)
DOJ litigation settlement	0	0
Contingent consideration	0	0
Derivative financial instruments, liabilities	(46)	(39)
Estimated Fair Value | Level 2 | Demand deposits and savings accounts
Liabilities
Deposits	(5,529)	(5,475)
Estimated Fair Value | Level 2 | Certificates of deposit
Liabilities
Deposits	(2,590)	(2,379)
Estimated Fair Value | Level 2 | Wholesale deposits
Liabilities
Deposits	(468)	(585)
Estimated Fair Value | Level 2 | Government deposits
Liabilities
Deposits	(1,116)	(1,145)
Estimated Fair Value | Level 2 | Custodial deposits
Liabilities
Deposits	(2,738)	(1,664)
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	10,085	8,958
Loans with government guarantees	0	0
Mortgage servicing rights	278	290
Federal Home Loan Bank stock	0	0
Bank owned life insurance	0	0
Repossessed assets	8	7
Other assets, foreclosure claims	0	0
Derivative financial instruments, assets	37	20
Liabilities
Federal Home Loan Bank advances	0	0
Long-term debt	0	0
DOJ litigation settlement	(60)	(60)
Contingent consideration	(6)	(6)
Derivative financial instruments, liabilities	0	0
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