Asset Quality - Additional Information (Details) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019 USD ($) SecurityLoan	Sep. 30, 2018 USD ($) SecurityLoan	Sep. 30, 2019 USD ($) SecurityLoan	Sep. 30, 2018 USD ($) SecurityLoan	Dec. 31, 2018 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision (credit) for losses on lending-related commitments	$ 1	$ 2	$ 1	$ 3
Percentage of carrying amount of our commercial nonperforming loans outstanding	77.00%		77.00%
Percentage of nonperforming loans outstanding face value	81.00%		81.00%
Percentage of loans held for sale and other nonperforming assets	84.00%		84.00%
Net reduction to interest income	$ 7	8	$ 24	22
Interest income recognized on outstanding balances	4	4	10	9
Commitments outstanding to lend additional funds to borrowers (less than $1 million)	1		1		$ 5
Financial receivable, modifications, subsequent default, recorded investment	1	$ 2	5	$ 4
Other real estate owned nonperforming loan	$ 39		$ 39		35
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	0	0	0	0
Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	79	82	255	178
Real Estate - Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivable, modifications, subsequent default, recorded investment			$ 104		$ 113