Asset Quality - Additional Information (Details) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019 USD ($) SecurityLoan	Mar. 31, 2018 USD ($) SecurityLoan	Dec. 31, 2018 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision (credit) for losses on lending-related commitments	$ (2)	$ 3
Percentage of carrying amount of our commercial nonperforming loans outstanding	79.00%
Percentage of nonperforming loans outstanding face value	82.00%
Percentage of loans held for sale and other nonperforming assets	86.00%
Net reduction to interest income	$ 8	7
Interest income recognized on outstanding balances	3	2
Commitments outstanding to lend additional funds to borrowers	4		$ 5
Financial receivable, modifications, subsequent default, recorded investment	2	$ 1
Other real estate owned nonperforming loan	$ 40		35
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	0	0
Consumer Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	74	41
Real Estate - Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivable, modifications, subsequent default, recorded investment	$ 96		113
Foreclosed Residential Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other real estate owned nonperforming loan	$ 39		$ 35