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Allowance for Loan Losses - Allowance for Credit Losses and Recorded Investments in Loans (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2017 USD ($) SecurityLoan	Mar. 31, 2016 USD ($) SecurityLoan
Allowance for Loan Losses
Beginning balance	$ 1,433	$ 1,564
Provision for loan losses	107	111
Charge-offs	(151)	(160)
Reclassification of interest reserve	2	3
Ending balance	1,391	1,518
Allowance:
Ending balance: individually evaluated for impairment	1,186	1,196
Ending balance: collectively evaluated for impairment	205	322
Loans:
Ending balance: individually evaluated for impairment	11,127	11,121
Ending balance: collectively evaluated for impairment	97,866	110,435
FFELP Loans [Member]
Allowance for Loan Losses
Beginning balance	67	78
Provision for loan losses	10	7
Charge-offs	(13)	(16)
Ending balance	64	69
Allowance:
Ending balance: collectively evaluated for impairment	64	69
Loans:
Ending balance: collectively evaluated for impairment	$ 84,513	$ 93,977
Charge-offs as a percentage of average loans in repayment (annualized)	0.07%	0.09%
Allowance coverage of charge-offs (annualized) | SecurityLoan	1.2	1.1
Allowance as a percentage of the ending total loan balance	0.08%	0.07%
Allowance as a percentage of the ending loans in repayment	0.09%	0.09%
Ending total loans	$ 84,513	$ 93,977
Average loans in repayment	69,302	73,697
Ending loans in repayment	68,095	73,630
Private Education Loans [Member]
Allowance for Loan Losses
Beginning balance	1,351	1,471
Provision for loan losses	95	104
Charge-offs	(137)	(144)
Reclassification of interest reserve	2	3
Ending balance	1,311	1,434
Allowance:
Ending balance: individually evaluated for impairment	1,176	1,185
Ending balance: collectively evaluated for impairment	135	249
Loans:
Ending balance: individually evaluated for impairment	11,096	11,088
Ending balance: collectively evaluated for impairment	$ 13,201	$ 16,408
Charge-offs as a percentage of average loans in repayment (annualized)	2.56%	2.39%
Allowance coverage of charge-offs (annualized) | SecurityLoan	2.4	2.5
Allowance as a percentage of the ending total loan balance	5.39%	5.22%
Allowance as a percentage of the ending loans in repayment	6.13%	6.03%
Ending total loans	$ 24,297	$ 27,496
Average loans in repayment	21,791	24,180
Ending loans in repayment	21,367	23,786
Other Loans [Member]
Allowance for Loan Losses
Beginning balance	15	15
Provision for loan losses	2
Charge-offs	(1)
Ending balance	16	15
Allowance:
Ending balance: individually evaluated for impairment	10	11
Ending balance: collectively evaluated for impairment	6	4
Loans:
Ending balance: individually evaluated for impairment	31	33
Ending balance: collectively evaluated for impairment	$ 152	$ 50
Charge-offs as a percentage of average loans in repayment (annualized)	2.06%	2.04%
Allowance coverage of charge-offs (annualized) | SecurityLoan	4.6	8.6
Allowance as a percentage of the ending total loan balance	9.00%	17.91%
Allowance as a percentage of the ending loans in repayment	9.00%	17.91%
Ending total loans	$ 183	$ 83
Average loans in repayment	173	85
Ending loans in repayment	$ 183	$ 83

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- Definition

Allowance as a percentage of the ending total loan balance.

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Allowance as a percentage of ending loans in repayment.

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Allowance coverage of charge-offs.

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Average balance of loans in repayment.

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Loans gross plus receivable for partially charged off loans.

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Total loans in repayment.

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Net charge offs as percentage of average loans in repayment.

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Amount of other addition (reduction) in allowance reserve for credit loss.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
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-Publisher FASB
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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount, after recoveries, of loans and leases that have been written-off.

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The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

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Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

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Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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Amount of expense related to estimated loss from loan and lease transactions.

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