Allowance for Loan Losses (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Allowance for Loan Losses
Beginning balance	$ 2,298,350	$ 2,283,555	$ 2,282,954	$ 1,680,869
Total provision	290,686	382,239	594,091	741,359
Charge-offs	(298,072)	(366,554)	(595,341)	(681,135)
Loan sales	(2,697)	(1,908)	(4,129)	(3,602)
Reclassification of interest reserve	6,927	10,292	17,619	20,934
Consolidation of securitization trusts				549,199
Ending Balance	2,295,194	2,307,624	2,295,194	2,307,624
Allowance:
Ending balance: individually evaluated for impairment	185,921	142,227	185,921	142,227
Ending balance: collectively evaluated for impairment	2,109,273	2,165,397	2,109,273	2,165,397
Ending balance: loans acquired with deteriorated credit quality	0	0	0	0
Loans
Ending balance: individually evaluated for impairment	665,960	486,593	665,960	486,593
Ending balance: collectively evaluated for impairment	179,334,464	183,929,471	179,334,464	183,929,471
Ending balance: loans acquired with deteriorated credit quality	0	0	0	0
FFELP Loans [Member]
Allowance for Loan Losses
Beginning balance	190,235	186,215	188,858	161,168
Total provision	22,313	28,613	45,435	51,609
Charge-offs	(20,827)	(24,235)	(41,140)	(45,639)
Loan sales	(2,697)	(1,908)	(4,129)	(3,602)
Consolidation of securitization trusts				25,149
Ending Balance	189,024	188,685	189,024	188,685
Allowance:
Ending balance: individually evaluated for impairment	0	0	0	0
Ending balance: collectively evaluated for impairment	189,024	188,685	189,024	188,685
Ending balance: loans acquired with deteriorated credit quality	0	0	0	0
Loans
Ending balance: individually evaluated for impairment	0	0	0	0
Ending balance: collectively evaluated for impairment	141,048,220	145,932,811	141,048,220	145,932,811
Ending balance: loans acquired with deteriorated credit quality	0	0	0	0
Charge-offs as a percentage of average loans in repayment and forbearance (annualized)	0.07%	0.10%	0.07%	0.09%
Charge-offs as a percentage of average loans in repayment (annualized)	0.09%	0.12%	0.09%	0.11%
Allowance as a percentage of the ending total loan balance	0.13%	0.13%	0.13%	0.13%
Allowance as a percentage of the ending loans in repayment	0.20%	0.23%	0.20%	0.23%
Allowance coverage of charge-offs (annualized)	2.3	1.9	2.3	2.1
Ending total loans	141,048,220	145,932,811	141,048,220	145,932,811
Average loans in repayment	94,317,705	82,449,191	94,907,800	82,443,391
Ending loans in repayment	94,282,103	82,978,473	94,282,103	82,978,473
Private Education Loans [Member]
Allowance for Loan Losses
Beginning balance	2,034,318	2,018,676	2,021,580	1,443,440
Total provision	264,938	349,211	539,986	674,233
Charge-offs	(263,580)	(335,766)	(536,582)	(620,244)
Reclassification of interest reserve	6,927	10,292	17,619	20,934
Consolidation of securitization trusts				524,050
Ending Balance	2,042,603	2,042,413	2,042,603	2,042,413
Allowance:
Ending balance: individually evaluated for impairment	133,796	81,867	133,796	81,867
Ending balance: collectively evaluated for impairment	1,908,807	1,960,546	1,908,807	1,960,546
Ending balance: loans acquired with deteriorated credit quality	0	0	0	0
Loans
Ending balance: individually evaluated for impairment	563,650	363,370	563,650	363,370
Ending balance: collectively evaluated for impairment	38,093,353	37,735,165	38,093,353	37,735,165
Ending balance: loans acquired with deteriorated credit quality	0	0	0	0
Charge-offs as a percentage of average loans in repayment and forbearance (annualized)	3.50%	5.10%	3.60%	4.80%
Charge-offs as a percentage of average loans in repayment (annualized)	3.70%	5.30%	3.80%	5.00%
Allowance as a percentage of the ending total loan balance	5.30%	5.40%	5.30%	5.40%
Allowance as a percentage of the ending loans in repayment	7.10%	7.90%	7.10%	7.90%
Allowance coverage of charge-offs (annualized)	1.9	1.5	1.9	1.6
Ending total loans	38,657,003	38,098,535	38,657,003	38,098,535
Average loans in repayment	28,488,734	25,178,957	28,308,899	24,913,768
Ending loans in repayment	28,871,968	25,721,573	28,871,968	25,721,573
Other loans [Member]
Allowance for Loan Losses
Beginning balance	73,797	78,664	72,516	76,261
Total provision	3,435	4,415	8,670	15,517
Charge-offs	(13,665)	(6,553)	(17,619)	(15,252)
Ending Balance	63,567	76,526	63,567	76,526
Allowance:
Ending balance: individually evaluated for impairment	52,125	60,360	52,125	60,360
Ending balance: collectively evaluated for impairment	11,442	16,166	11,442	16,166
Ending balance: loans acquired with deteriorated credit quality	0	0	0	0
Loans
Ending balance: individually evaluated for impairment	102,310	123,223	102,310	123,223
Ending balance: collectively evaluated for impairment	192,891	261,495	192,891	261,495
Ending balance: loans acquired with deteriorated credit quality	0	0	0	0
Allowance as a percentage of the ending total loan balance	21.50%	19.90%	21.50%	19.90%
Allowance coverage of charge-offs (annualized)	1.2	2.9	1.8	2.5
Ending total loans	295,201	384,718	295,201	384,718
Ending loans in repayment	$ 0	$ 0	$ 0	$ 0