Fair Value Of Financial Instruments (Aggregate Fair Value And Remaining Contractual Principal Balance Outstanding On Fair Value Option) (Detail) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
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	$ 169	$ 217
Medium-term notes, fair value	106	161
Medium-term notes, difference	63	56
Variable Interest Entity [Member]
Schedule Of Fair Value Of Separate Accounts By Major Category Of Investment [Line Items]
Loans receivable, contractual outstanding principal	1,351	1,619
Variable interest entity notes, contractual outstanding principal	2,551	3,663
Loans receivable, fair value	1,142	1,292
Variable interest entity notes, fair value	1,433	2,362
Loans receivable, difference	209	327
Variable interest entity notes, difference	1,118	1,301
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	1,054	1,260
Loans receivable, 90 days or more past due, contractual outstanding principal	150	177
Loans receivable, fair value	962	1,149
Loans receivable, 90 days or more past due, fair value	33	36
Loans receivable, difference	92	111
Loans receivable, 90 days or more past due, difference	117	141
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	0	107
Loans receivable, 90 days or more past due, contractual outstanding principal	147	75
Loans receivable, fair value	0	107
Loans receivable, 90 days or more past due, fair value	147	0
Loans receivable, difference	0	0
Loans receivable, 90 days or more past due, difference	$ 0	$ 75