Loans Held for Sale - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale		$ 289	$ 512
Revenue associated with the economic hedging program (less than)		2,082	(1,131)	$ 1,136
Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale		212	394
Valuation allowance		0	3
Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale		77	118
Valuation allowance		2	4
Commercial Loans - Fair Value Option [Member] | Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale		178	109
Commercial Loans - Transferred to Held for Sale [Member] | Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale		34	285
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
Residential Mortgage [Member] | Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale		77	65
Other Income (Loss) [Member] | Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Lower of amortized cost or fair value adjustment		0	(5)	$ (5)
Residential mortgage banking revenue (expense) [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenue associated with the economic hedging program (less than)		$ (1)	$ (1)