Fair Value Of Financial Instruments (Aggregate Fair Value And Remaining Contractual Principal Balance Outstanding On Fair Value Option) (Detail) - Variable Interest Entity [Member] - Loans Receivable [Member] - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Residential Mortgage Loans [Member]
Schedule Of Fair Value Of Separate Accounts By Major Category Of Investment [Line Items]
Loans receivable and other instruments, contractual outstanding principal	$ 96	$ 107
Loans receivable and other instruments, 90 days or more past due, contractual outstanding principal	123	154
Loans receivable and other instruments, fair value	87	107
Loans receivable and other instruments, 90 days or more past due, fair value	11	29
Loans receivable and other instruments, difference	9	0
Loans receivable and other instruments, 90 days or more past due, difference	112	125
Medium Term Notes [Member]
Schedule Of Fair Value Of Separate Accounts By Major Category Of Investment [Line Items]
Long-term debt instruments, contractual outstanding principal	110	112
Long-term debt instruments, fair value	98	108
Long-term debt instruments, difference	12	4
Variable Interest Entity Notes [Member]
Schedule Of Fair Value Of Separate Accounts By Major Category Of Investment [Line Items]
Long-term debt instruments, contractual outstanding principal	1,097	1,126
Long-term debt instruments, fair value	331	403
Long-term debt instruments, difference	766	723
Total Loans Receivable and Other Instruments [Member]
Schedule Of Fair Value Of Separate Accounts By Major Category Of Investment [Line Items]
Loans receivable and other instruments, contractual outstanding principal	219	261
Loans receivable and other instruments, fair value	98	136
Loans receivable and other instruments, difference	$ 121	$ 125