Fair Value Of Financial Instruments (Aggregate Fair Value And Remaining Contractual Principal Balance Outstanding On Fair Value Option) (Detail) - Variable Interest Entity [Member] - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Schedule Of Fair Value Of Separate Accounts By Major Category Of Investment [Line Items]
Loans receivable, contractual outstanding principal	$ 2,270	$ 2,296
Loans receivable, fair value	1,662	1,679
Loans receivable, difference	608	617
Residential Mortgage Loans [Member]
Schedule Of Fair Value Of Separate Accounts By Major Category Of Investment [Line Items]
Loans receivable, contractual outstanding principal	687	732
Loans receivable, 90 days or more past due, contractual outstanding principal	189	170
Loans receivable, fair value	686	727
Loans receivable, 90 days or more past due, fair value	51	32
Loans receivable, difference	1	5
Loans receivable, 90 days or more past due, difference	138	138
Corporate Loans [Member]
Schedule Of Fair Value Of Separate Accounts By Major Category Of Investment [Line Items]
Loans receivable, 90 days or more past due, contractual outstanding principal	1,394	1,394
Loans receivable, 90 days or more past due, fair value	925	920
Loans receivable, 90 days or more past due, difference	469	474
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	184	180
Long-term debt instruments, fair value	146	115
Long-term debt instruments, difference	39	65
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	1,848	1,882
Long-term debt instruments, fair value	1,031	1,069
Long-term debt instruments, difference	$ 817	$ 813