Loans Receivable, Net - Overall Statistics for Loans Receivable Portfolio (Parenthetical) (Detail) - USD ($) $ in Billions	Mar. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of loans subject to yield maintenance, or other prepayment restrictions	57.00%	61.00%
Percentage of loans open to repayment by borrower without penalty	43.00%	39.00%
USD LIBOR [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of loans receivable by type	99.00%	99.00%
Percentage of loans, fixed rate	1.00%
Additional loan receivable of floating rate	$ 11.1	$ 6.1