Description of Business, Basis of Presentation, and Summary of Significant Accounting Policies - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	$ 46	$ 31
Deposit account and other banking income | Community Banking | Deposit fees and charges
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	27	16
Interchange fees | Community Banking | Deposit fees and charges
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	11	5
Interchange fees | Community Banking | Other noninterest income
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	2	1
Wealth management | Community Banking | Other noninterest income
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	$ 6	$ 9