Acquisitions and Discontinued Operations - Consolidated Assets and Liabilities at Fair Value on Recurring Basis (Detail) (Recurring [Member], USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012
ASSETS MEASURED ON A RECURRING BASIS
Total assets at fair value	$ 15,325	$ 14,334	$ 15,961
LIABILITIES MEASURED ON A RECURRING BASIS
Total liabilities on a recurring basis at fair value	1,107	1,148	1,611
Segment, Discontinued Operations [Member] | Education Lending [Member]
ASSETS MEASURED ON A RECURRING BASIS
Portfolio loans	151
Trust loans	2,317
Trust other assets	24
Total assets at fair value	2,492
LIABILITIES MEASURED ON A RECURRING BASIS
Trust securities	2,118
Trust other liabilities	21
Total liabilities on a recurring basis at fair value	2,139
Level 1 [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total assets at fair value	117	99	117
LIABILITIES MEASURED ON A RECURRING BASIS
Total liabilities on a recurring basis at fair value	82	55	84
Level 1 [Member] | Segment, Discontinued Operations [Member] | Education Lending [Member]
ASSETS MEASURED ON A RECURRING BASIS
Portfolio loans
Trust loans
Trust other assets
Total assets at fair value
LIABILITIES MEASURED ON A RECURRING BASIS
Trust securities
Trust other liabilities
Total liabilities on a recurring basis at fair value
Level 2 [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total assets at fair value	15,525	14,808	16,353
LIABILITIES MEASURED ON A RECURRING BASIS
Total liabilities on a recurring basis at fair value	1,657	1,894	2,405
Level 2 [Member] | Segment, Discontinued Operations [Member] | Education Lending [Member]
ASSETS MEASURED ON A RECURRING BASIS
Portfolio loans
Trust loans
Trust other assets
Total assets at fair value
LIABILITIES MEASURED ON A RECURRING BASIS
Trust securities
Trust other liabilities
Total liabilities on a recurring basis at fair value
Level 3 [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total assets at fair value	675	697	873
LIABILITIES MEASURED ON A RECURRING BASIS
Total liabilities on a recurring basis at fair value	1	2	2
Level 3 [Member] | Segment, Discontinued Operations [Member] | Education Lending [Member]
ASSETS MEASURED ON A RECURRING BASIS
Portfolio loans	151
Trust loans	2,317
Trust other assets	24
Total assets at fair value	2,492
LIABILITIES MEASURED ON A RECURRING BASIS
Trust securities	2,118
Trust other liabilities	21
Total liabilities on a recurring basis at fair value	$ 2,139