Fair Value Of Financial Instruments (Aggregate Fair Value And Remaining Contractual Principal Balance Outstanding On Fair Value Option) (Detail) - USD ($) $ in Millions	Jun. 30, 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	$ 171	$ 158
Medium-term notes, fair value	123	101
Medium-term notes, difference	48	57
Variable Interest Entity [Member]
Schedule Of Fair Value Of Separate Accounts By Major Category Of Investment [Line Items]
Loans receivable, contractual outstanding principal	1,865	1,258
Variable interest entity notes, contractual outstanding principal	3,065	2,449
Loans receivable, fair value	1,690	1,066
Variable interest entity notes, fair value	1,261	1,351
Loans receivable, difference	175	192
Variable interest entity notes, difference	1,804	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	828	965
Loans receivable, 90 days or more past due, contractual outstanding principal	162	143
Loans receivable, fair value	779	894
Loans receivable, 90 days or more past due, fair value	36	22
Loans receivable, difference	49	71
Loans receivable, 90 days or more past due, difference	126	121
Corporate 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	875	150
Loans receivable, fair value	0	0
Loans receivable, 90 days or more past due, fair value	875	150
Loans receivable, difference	0	0
Loans receivable, 90 days or more past due, difference	$ 0	$ 0