Fair Value Of Financial Instruments (Aggregate Fair Value And Remaining Contractual Principal Balance Outstanding On Fair Value Option) (Detail) - USD ($) $ in Millions	Dec. 31, 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	$ 158	$ 217
Medium-term notes, fair value	101	161
Medium-term notes, difference	57	56
Variable Interest Entity [Member]
Schedule Of Fair Value Of Separate Accounts By Major Category Of Investment [Line Items]
Loans receivable, contractual outstanding principal	1,258	1,619
Variable interest entity notes, contractual outstanding principal	2,449	3,663
Loans receivable, fair value	1,066	1,292
Variable interest entity notes, fair value	1,351	2,362
Loans receivable, difference	192	327
Variable interest entity notes, difference	1,098	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	965	1,260
Loans receivable, 90 days or more past due, contractual outstanding principal	143	177
Loans receivable, fair value	894	1,149
Loans receivable, 90 days or more past due, fair value	22	36
Loans receivable, difference	71	111
Loans receivable, 90 days or more past due, difference	121	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	150	75
Loans receivable, fair value	0	107
Loans receivable, 90 days or more past due, fair value	150	0
Loans receivable, difference	0	0
Loans receivable, 90 days or more past due, difference	$ 0	$ 75