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Summary of Portfolio of Securities Held to Maturity (Detail) - USD ($) $ in Thousands | Dec. 31, 2016 | Dec. 31, 2015
--- | --- | ---
Schedule of Held-to-maturity Securities [Line Items] |  |  |  |
Amortized Cost | $ 3,721,368 | [1] | $ 5,978,107 | [2]
Carrying Amount | 3,712,776 | [1] | 5,969,390 | [2]
Gross Unrealized Gain | 117,373 | [1] | 168,470 | [2]
Gross Unrealized Loss | 16,190 | [1] | 29,331 | [2]
Fair Value | 3,813,959 | [1] | 6,108,529 | [2]
Mortgage-Related Securities |  |  |  |
Schedule of Held-to-maturity Securities [Line Items] |  |  |  |
Amortized Cost | 3,212,563 |  | 3,594,861 |
Carrying Amount | 3,212,563 |  | 3,594,861 |
Gross Unrealized Gain | 101,326 |  | 130,063 |
Gross Unrealized Loss | 2,456 |  | 4,779 |
Fair Value | 3,311,433 |  | 3,720,145 |
Mortgage-Related Securities | GSE certificates |  |  |  |
Schedule of Held-to-maturity Securities [Line Items] |  |  |  |
Amortized Cost | 2,193,489 |  | 2,269,828 |
Carrying Amount | 2,193,489 |  | 2,269,828 |
Gross Unrealized Gain | 64,431 |  | 76,827 |
Gross Unrealized Loss | 2,399 |  | 4,722 |
Fair Value | 2,255,521 |  | 2,341,933 |
Mortgage-Related Securities | GSE CMOs |  |  |  |
Schedule of Held-to-maturity Securities [Line Items] |  |  |  |
Amortized Cost | 1,019,074 | [3] | 1,325,033 |
Carrying Amount | 1,019,074 | [3] | 1,325,033 |
Gross Unrealized Gain | 36,895 | [3] | 53,236 |
Gross Unrealized Loss | 57 | [3] | 57 |
Fair Value | 1,055,912 | [3] | 1,378,212 |
Other Securities |  |  |  |
Schedule of Held-to-maturity Securities [Line Items] |  |  |  |
Amortized Cost | 508,805 |  | 2,383,246 |
Carrying Amount | 500,213 |  | 2,374,529 |
Gross Unrealized Gain | 16,047 |  | 38,407 |
Gross Unrealized Loss | 13,734 |  | 24,552 |
Fair Value | 502,526 |  | 2,388,384 |
Other Securities | U.S. Treasury obligations |  |  |  |
Schedule of Held-to-maturity Securities [Line Items] |  |  |  |
Amortized Cost | 200,293 |  |  |
Carrying Amount | 200,293 |  |  |
Gross Unrealized Loss | 73 |  |  |
Fair Value | 200,220 |  |  |
Other Securities | GSE debentures |  |  |  |
Schedule of Held-to-maturity Securities [Line Items] |  |  |  |
Amortized Cost | 88,457 |  | 2,159,856 |
Carrying Amount | 88,457 |  | 2,159,856 |
Gross Unrealized Gain | 3,836 |  | 23,892 |
Gross Unrealized Loss |  |  | 7,568 |
Fair Value | 92,293 |  | 2,176,180 |
Other Securities | Corporate bonds |  |  |  |
Schedule of Held-to-maturity Securities [Line Items] |  |  |  |
Amortized Cost | 74,217 |  | 73,756 |
Carrying Amount | 74,217 |  | 73,756 |
Gross Unrealized Gain | 9,549 |  | 10,503 |
Fair Value | 83,766 |  | 84,259 |
Other Securities | Municipal bonds |  |  |  |
Schedule of Held-to-maturity Securities [Line Items] |  |  |  |
Amortized Cost | 71,554 |  | 75,317 |
Carrying Amount | 71,554 |  | 75,317 |
Gross Unrealized Gain |  |  | 262 |
Gross Unrealized Loss | 1,789 |  | 1,084 |
Fair Value | 69,765 |  | 74,495 |
Other Securities | Capital trust notes |  |  |  |
Schedule of Held-to-maturity Securities [Line Items] |  |  |  |
Amortized Cost | 74,284 |  | 74,317 |
Carrying Amount | 65,692 |  | 65,600 |
Gross Unrealized Gain | 2,662 |  | 3,750 |
Gross Unrealized Loss | 11,872 |  | 15,900 |
Fair Value | $ 56,482 |  | $ 53,450 |
[1] | Held-to-maturity securities are reported at a carrying amount equal to amortized cost less the non-credit portion of OTTI recorded in AOCL. At December 31, 2016, the non-credit portion of OTTI recorded in AOCL was $8.6 million (before taxes).
[2] | Held-to-maturity securities are reported at a carrying amount equal to amortized cost less the non-credit portion of OTTI recorded in AOCL. At December 31, 2015, the non-credit portion of OTTI recorded in AOCL was $8.7 million (before taxes).
[3] | Collateralized mortgage obligations.

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