Loans - Summary of Consumer Loans by Refreshed FICO Credit Score (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Recorded Investment [Line Items]
Total loans, gross	$ 131,321	$ 110,345
Percentage concentration of gross installment and credit card loans by refreshed FICO credit score	100.00%	100.00%
FICO [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, gross	$ 6,907	$ 6,605
Percentage concentration of gross installment and credit card loans by refreshed FICO credit score	100.00%	100.00%
Installment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, gross	$ 4,826	$ 4,747
Installment [Member] | FICO [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, gross	4,826	4,747
Credit cards [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, gross	$ 2,081	$ 1,858
Percentage concentration of gross installment and credit card loans by refreshed FICO credit score	100.00%	100.00%
Credit cards [Member] | FICO [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, gross	$ 2,081	$ 1,858
Greater than or equal to 660 [Member] | FICO [Member]
Financing Receivable, Recorded Investment [Line Items]
Percentage concentration of gross installment and credit card loans by refreshed FICO credit score	82.00%	85.00%
Less than 660 [Member] | FICO [Member]
Financing Receivable, Recorded Investment [Line Items]
Percentage concentration of gross installment and credit card loans by refreshed FICO credit score	18.00%	15.00%