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	Jun. 30, 2019	Dec. 31, 2018
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	$ 115	$ 168
Loans receivable and other instruments, 90 days or more past due, contractual outstanding principal	152	153
Loans receivable and other instruments, fair value	115	164
Loans receivable and other instruments, 90 days or more past due, fair value	39	8
Loans receivable and other instruments, difference	0	4
Loans receivable and other instruments, 90 days or more past due, difference	113	145
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	113	114
Long-term debt instruments, fair value	110	102
Long-term debt instruments, difference	3	12
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	1,854	1,295
Long-term debt instruments, fair value	1,120	480
Long-term debt instruments, difference	734	815
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	267	321
Loans receivable and other instruments, fair value	154	172
Loans receivable and other instruments, difference	$ 113	$ 149