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, 2013	Dec. 31, 2012	Mar. 31, 2012
ASSETS MEASURED ON A RECURRING BASIS
Total assets at fair value	$ 15,879	$ 14,334	$ 17,273
LIABILITIES MEASURED ON A RECURRING BASIS
Total liabilities on a recurring basis at fair value	1,395	1,148	1,480
Segment, discontinued operations [Member] | Education lending [Member]
ASSETS MEASURED ON A RECURRING BASIS
Portfolio loans	154
Trust loans	2,333
Trust other assets	25
Total assets at fair value	2,512
LIABILITIES MEASURED ON A RECURRING BASIS
Trust securities	2,126
Trust other liabilities	25
Total liabilities on a recurring basis at fair value	2,151
Level 1 [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total assets at fair value	107	99	115
LIABILITIES MEASURED ON A RECURRING BASIS
Total liabilities on a recurring basis at fair value	57	55	70
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	16,182	14,808	17,642
LIABILITIES MEASURED ON A RECURRING BASIS
Total liabilities on a recurring basis at fair value	2,032	1,894	2,255
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	705	697	811
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	154
Trust loans	2,333
Trust other assets	25
Total assets at fair value	2,512
LIABILITIES MEASURED ON A RECURRING BASIS
Trust securities	2,126
Trust other liabilities	25
Total liabilities on a recurring basis at fair value	$ 2,151