Acquisitions and Discontinued Operations - Consolidated Assets and Liabilities at Fair Value on Recurring Basis (Detail) (Recurring [Member], USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
ASSETS MEASURED ON A RECURRING BASIS
Total assets at fair value	$ 15,026	$ 15,135	$ 14,190
LIABILITIES MEASURED ON A RECURRING BASIS
Total liabilities on a recurring basis at fair value	1,434	1,207	871
Trust [Member] | Education Lending [Member]
ASSETS MEASURED ON A RECURRING BASIS
Portfolio loans	187	191	143
Trust loans			1,893
Trust other assets			19
Total assets at fair value	187	191	2,055
LIABILITIES MEASURED ON A RECURRING BASIS
Trust securities			1,796
Trust other liabilities			20
Total liabilities on a recurring basis at fair value			1,816
Level 3 [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total assets at fair value	406	440	590
LIABILITIES MEASURED ON A RECURRING BASIS
Total liabilities on a recurring basis at fair value	1	1	1
Level 3 [Member] | Trust [Member] | Education Lending [Member]
ASSETS MEASURED ON A RECURRING BASIS
Portfolio loans	187	191	143
Trust loans			1,893
Trust other assets			19
Total assets at fair value	187	191	2,055
LIABILITIES MEASURED ON A RECURRING BASIS
Trust securities			1,796
Trust other liabilities			20
Total liabilities on a recurring basis at fair value			$ 1,816