Fair Value Of Financial Instruments (Aggregate Fair Value And Remaining Contractual Principal Balance Outstanding On Fair Value Option) (Detail) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Non Variable Interest Entity [Member]
Schedule Of Fair Value Of Separate Accounts By Major Category Of Investment [Line Items]
Medium-term notes, contractual outstanding principal	$ 223	$ 242
Medium-term notes, fair value	170	197
Medium-term notes, difference	53	45
Variable Interest Entity [Member]
Schedule Of Fair Value Of Separate Accounts By Major Category Of Investment [Line Items]
Loans receivable, contractual outstanding principal	1,705	2,502
Variable interest entity notes, contractual outstanding principal	3,758	3,584
Loans receivable, fair value	1,351	2,142
Variable interest entity notes, fair value	2,460	2,479
Loans receivable, difference	354	360
Variable interest entity notes, difference	1,298	1,105
Residential Mortgage Loans [Member] | Variable Interest Entity [Member]
Schedule Of Fair Value Of Separate Accounts By Major Category Of Investment [Line Items]
Loans receivable, contractual outstanding principal	1,331	1,554
Loans receivable, 90 days or more past due, contractual outstanding principal	194	227
Loans receivable, fair value	1,233	1,377
Loans receivable, 90 days or more past due, fair value	11	54
Loans receivable, difference	98	177
Loans receivable, 90 days or more past due, difference	183	173
Other Loans [Member] | Variable Interest Entity [Member]
Schedule Of Fair Value Of Separate Accounts By Major Category Of Investment [Line Items]
Loans receivable, contractual outstanding principal	107	721
Loans receivable, 90 days or more past due, contractual outstanding principal	73
Loans receivable, fair value	107	711
Loans receivable, difference	0	$ 10
Loans receivable, 90 days or more past due, difference	$ 73