Fair Value Of Financial Instruments (Aggregate Fair Value And Remaining Contractual Principal Balance Outstanding On Fair Value Option) (Detail) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
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	$ 160	$ 158
Medium-term notes, fair value	104	101
Medium-term notes, difference	56	57
Variable Interest Entity [Member]
Schedule Of Fair Value Of Separate Accounts By Major Category Of Investment [Line Items]
Loans receivable, contractual outstanding principal	1,943	1,258
Variable interest entity notes, contractual outstanding principal	3,152	2,449
Loans receivable, fair value	1,716	1,066
Variable interest entity notes, fair value	1,306	1,351
Loans receivable, difference	227	192
Variable interest entity notes, difference	1,846	1,098
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	890	965
Loans receivable, 90 days or more past due, contractual outstanding principal	163	143
Loans receivable, fair value	822	894
Loans receivable, 90 days or more past due, fair value	22	22
Loans receivable, difference	68	71
Loans receivable, 90 days or more past due, difference	141	121
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	0
Loans receivable, 90 days or more past due, contractual outstanding principal	890	150
Loans receivable, fair value	0	0
Loans receivable, 90 days or more past due, fair value	872	150
Loans receivable, difference	0	0
Loans receivable, 90 days or more past due, difference	$ 18	$ 0