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Allowance for Loan Losses - Allowance for Credit Losses and Recorded Investments in Loans (Detail) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2016 USD ($) SecurityLoan | Jun. 30, 2015 USD ($) SecurityLoan | Jun. 30, 2016 USD ($) SecurityLoan | Jun. 30, 2015 USD ($) SecurityLoan
Allowance for Loan Losses |  |  |  |
Beginning balance | $ 1,519 | $ 1,963 | $ 1,564 | $ 2,033
Total provision | 110 | 198 | 221 | 323
Net adjustment resulting from the change in the charge-off rate |  | (330) |  | (330)
Net charge-offs remaining |  | (190) |  | (388)
Charge-offs | (145) | (520) | (304) | (718)
Reclassification of interest reserve | 3 | 2 | 6 | 5
Ending balance | 1,487 | 1,643 | 1,487 | 1,643
Allowance: |  |  |  |
Ending balance: individually evaluated for impairment | 1,174 | 1,274 | 1,174 | 1,274
Ending balance: collectively evaluated for impairment | 313 | 369 | 313 | 369
Loans: |  |  |  |
Ending balance: individually evaluated for impairment | 11,195 | 10,810 | 11,195 | 10,810
Ending balance: collectively evaluated for impairment | 107,244 | 118,697 | 107,244 | 118,697
FFELP Loans [Member] |  |  |  |
Allowance for Loan Losses |  |  |  |
Beginning balance | 70 | 91 | 78 | 93
Total provision | 10 | 7 | 17 | 12
Net charge-offs remaining |  | (9) |  | (16)
Charge-offs | (18) | (9) | (33) | (16)
Ending balance | 62 | 89 | 62 | 89
Allowance: |  |  |  |
Ending balance: collectively evaluated for impairment | 62 | 89 | 62 | 89
Loans: |  |  |  |
Ending balance: collectively evaluated for impairment | $ 91,719 | $ 99,207 | $ 91,719 | $ 99,207
Net charge-offs as a percentage of average loans in repayment, excluding the net adjustment resulting from the change in the charge-off rate (annualized) |  | 0.05% |  | 0.04%
Charge-offs as a percentage of average loans in repayment (annualized) | 0.10% |  | 0.09% |
Allowance coverage of charge-offs (annualized) | SecurityLoan | 0.9 |  | 1.0 |
Allowance coverage of net charge-offs, excluding the net adjustment resulting from the change in the charge-off rate (annualized) | SecurityLoan |  | 2.3 |  | 2.8
Allowance as a percentage of the ending total loan balance | 0.07% | 0.09% | 0.07% | 0.09%
Allowance as a percentage of the ending loans in repayment | 0.09% | 0.12% | 0.09% | 0.12%
Ending total loans | $ 91,719 | $ 99,207 | $ 91,719 | $ 99,207
Average loans in repayment | 72,973 | 76,325 | 73,331 | 76,896
Ending loans in repayment | 72,058 | 75,244 | 72,058 | 75,244
Private Education Loans [Member] |  |  |  |
Allowance for Loan Losses |  |  |  |
Beginning balance | 1,434 | 1,849 | 1,471 | 1,916
Total provision | 100 | 191 | 204 | 311
Net adjustment resulting from the change in the charge-off rate |  | (330) |  | (330)
Net charge-offs remaining |  | (179) |  | (369)
Charge-offs | (127) | (509) | (271) | (699)
Reclassification of interest reserve | 3 | 2 | 6 | 5
Ending balance | 1,410 | 1,533 | 1,410 | 1,533
Allowance: |  |  |  |
Ending balance: individually evaluated for impairment | 1,163 | 1,257 | 1,163 | 1,257
Ending balance: collectively evaluated for impairment | 247 | 276 | 247 | 276
Loans: |  |  |  |
Ending balance: individually evaluated for impairment | 11,162 | 10,769 | 11,162 | 10,769
Ending balance: collectively evaluated for impairment | $ 15,478 | $ 19,435 | $ 15,478 | $ 19,435
Net charge-offs as a percentage of average loans in repayment, excluding the net adjustment resulting from the change in the charge-off rate (annualized) |  | 2.74% |  | 2.82%
Charge-offs as a percentage of average loans in repayment (annualized) | 2.17% |  | 2.28% |
Net adjustment resulting from the change in the charge-off rate as a percentage of average loans in repayment (annualized) |  | 5.07% |  | 2.53%
Allowance coverage of charge-offs (annualized) | SecurityLoan | 2.8 |  | 2.6 |
Allowance coverage of net charge-offs, excluding the net adjustment resulting from the change in the charge-off rate (annualized) | SecurityLoan |  | 2.1 |  | 2.1
Allowance as a percentage of the ending total loan balance | 5.29% | 5.08% | 5.29% | 5.08%
Allowance as a percentage of the ending loans in repayment | 6.06% | 5.93% | 6.06% | 5.93%
Ending total loans | $ 26,640 | $ 30,204 | $ 26,640 | $ 30,204
Average loans in repayment | 23,561 | 26,122 | 23,871 | 26,382
Ending loans in repayment | 23,265 | 25,865 | 23,265 | 25,865
Other Loans [Member] |  |  |  |
Allowance for Loan Losses |  |  |  |
Beginning balance | 15 | 23 | 15 | 24
Net charge-offs remaining |  | (2) |  | (3)
Charge-offs |  | (2) |  | (3)
Ending balance | 15 | 21 | 15 | 21
Allowance: |  |  |  |
Ending balance: individually evaluated for impairment | 11 | 17 | 11 | 17
Ending balance: collectively evaluated for impairment | 4 | 4 | 4 | 4
Loans: |  |  |  |
Ending balance: individually evaluated for impairment | 33 | 41 | 33 | 41
Ending balance: collectively evaluated for impairment | $ 47 | $ 55 | $ 47 | $ 55
Net charge-offs as a percentage of average loans in repayment, excluding the net adjustment resulting from the change in the charge-off rate (annualized) |  | 8.68% |  | 6.01%
Charge-offs as a percentage of average loans in repayment (annualized) | 1.32% |  | 1.69% |
Allowance coverage of charge-offs (annualized) | SecurityLoan | 13.5 |  | 10.4 |
Allowance coverage of net charge-offs, excluding the net adjustment resulting from the change in the charge-off rate (annualized) | SecurityLoan |  | 2.4 |  | 3.3
Allowance as a percentage of the ending total loan balance | 18.18% | 21.50% | 18.18% | 21.50%
Allowance as a percentage of the ending loans in repayment | 18.18% | 21.50% | 18.18% | 21.50%
Ending total loans | $ 80 | $ 96 | $ 80 | $ 96
Average loans in repayment | 82 | 101 | 83 | 103
Ending loans in repayment | $ 80 | $ 96 | $ 80 | $ 96

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- Definition Amount of other addition (reduction) in allowance reserve for credit loss. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5212-111524 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.7(d)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
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- Definition The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953423-111524 + Details
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- Definition 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. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953423-111524 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953423-111524 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.7(d)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section S99 -Paragraph 4 -Subparagraph (SAB Topic 6.L.1) -URI http://asc.fasb.org/extlink&oid=27010918&loc=d3e74567-122707 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (b)(1)(ii) -URI http://asc.fasb.org/extlink&oid=6379141&loc=d3e15032-111544 + Details
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