Acquisitions and Discontinued Operations - Consolidated Assets and Liabilities at Fair Value on Recurring Basis (Detail) (Recurring [Member], USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
ASSETS MEASURED ON A RECURRING BASIS
Total assets at fair value	$ 15,135	$ 14,069
LIABILITIES MEASURED ON A RECURRING BASIS
Total liabilities on a recurring basis at fair value	1,207	758
Trust [Member] | Education Lending [Member]
ASSETS MEASURED ON A RECURRING BASIS
Portfolio loans	191	147
Trust loans		1,960
Trust other assets		20
Total assets at fair value	191	2,127
LIABILITIES MEASURED ON A RECURRING BASIS
Trust securities		1,834
Trust other liabilities		20
Total liabilities on a recurring basis at fair value		1,854
Level 3 [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total assets at fair value	440	606
LIABILITIES MEASURED ON A RECURRING BASIS
Total liabilities on a recurring basis at fair value	1	1
Level 3 [Member] | Trust [Member] | Education Lending [Member]
ASSETS MEASURED ON A RECURRING BASIS
Portfolio loans	191	147
Trust loans		1,960
Trust other assets		20
Total assets at fair value	191	2,127
LIABILITIES MEASURED ON A RECURRING BASIS
Trust securities		1,834
Trust other liabilities		20
Total liabilities on a recurring basis at fair value		$ 1,854