Acquisitions and Discontinued Operations - Consolidated Assets and Liabilities at Fair Value on Recurring Basis (Detail) (Recurring [Member], USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
ASSETS MEASURED ON A RECURRING BASIS
Total assets at fair value	$ 15,064	$ 14,334	$ 14,539
LIABILITIES MEASURED ON A RECURRING BASIS
Total liabilities on a recurring basis at fair value	1,509	1,148	1,444
Segment, Discontinued Operations [Member] | Education Lending [Member]
ASSETS MEASURED ON A RECURRING BASIS
Portfolio loans	148
Trust loans	2,135
Trust other assets	23
Total assets at fair value	2,306
LIABILITIES MEASURED ON A RECURRING BASIS
Trust securities	2,016
Trust other liabilities	21
Total liabilities on a recurring basis at fair value	2,037
Level 1 [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total assets at fair value	90	99	89
LIABILITIES MEASURED ON A RECURRING BASIS
Total liabilities on a recurring basis at fair value	63	55	61
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	15,207	14,808	15,029
LIABILITIES MEASURED ON A RECURRING BASIS
Total liabilities on a recurring basis at fair value	2,003	1,894	2,286
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	636	697	797
LIABILITIES MEASURED ON A RECURRING BASIS
Total liabilities on a recurring basis at fair value	2	2	2
Level 3 [Member] | Segment, Discontinued Operations [Member] | Education Lending [Member]
ASSETS MEASURED ON A RECURRING BASIS
Portfolio loans	148
Trust loans	2,135
Trust other assets	23
Total assets at fair value	2,306
LIABILITIES MEASURED ON A RECURRING BASIS
Trust securities	2,016
Trust other liabilities	21
Total liabilities on a recurring basis at fair value	$ 2,037