Loans Receivable - Summary of Loans Receivable - Percentage Concentration Gross Loan Credit Score (Detail) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 87,158	$ 81,656
Consumer loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 5,525	$ 4,536
Percentage concentration of gross consumer loans by refreshed FICO credit score	100.00%	100.00%
Greater than or equal to 660 [Member] | Consumer loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Percentage concentration of gross consumer loans by refreshed FICO credit score	87.00%	88.00%
Less than 660 [Member] | Consumer loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Percentage concentration of gross consumer loans by refreshed FICO credit score	13.00%	12.00%