Acquisitions and Discontinued Operations - Consolidated Assets at Fair Value on Recurring Basis (Detail) - Recurring [Member] - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
ASSETS MEASURED ON A RECURRING BASIS
Total assets at fair value	$ 16,332	$ 15,139	$ 14,108
Trust [Member] | Education Lending [Member]
ASSETS MEASURED ON A RECURRING BASIS
Portfolio loans held for sale	169
Portfolio loans		191	201
Total assets at fair value	169	191	201
Level 3 [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total assets at fair value	392	444	517
Level 3 [Member] | Trust [Member] | Education Lending [Member]
ASSETS MEASURED ON A RECURRING BASIS
Portfolio loans held for sale	169
Portfolio loans		191	201
Total assets at fair value	$ 169	$ 191	$ 201