Loans Held for Sale - Additional Information (Details) - USD ($)	3 Months Ended			9 Months Ended
	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale	$ 540,000,000			$ 540,000,000		$ 512,000,000
Revenue associated with the economic hedging program (less than)	189,000,000		$ 193,000,000	1,738,000,000	$ (209,000,000)
Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale	482,000,000			482,000,000		394,000,000
Valuation allowance	0			0		3,000,000
Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale	58,000,000			58,000,000		118,000,000
Valuation allowance	2,000,000			2,000,000		4,000,000
Commercial Loans - Fair Value Option [Member] | Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale	389,000,000			389,000,000		109,000,000
Commercial Loans - Transferred to Held for Sale [Member] | Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale	93,000,000			93,000,000		$ 285,000,000
Student Loans [Member] | Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Transfer of loans held-for-sale to loans held for investment		$ 53,000,000
Other Income (Loss) [Member] | Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Lower of amortized cost or fair value adjustment	0		(2,000,000)	0	(5,000,000)
Residential mortgage banking revenue (expense) [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenue associated with the economic hedging program (less than)	$ 1,000,000		$ 1,000,000	$ 1,000,000	$ 1,000,000