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Business Segments (Summary Of Company's Segment Results) (Detail) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Segment Reporting Information [Line Items] |  |  |  |  |  |  |
Revenues |  | $ 480 | [1] | $ 530 | [1] | $ 616 | [2]
Net change in fair value of insured derivatives |  | (19) |  | 129 |  | 459 |
Net gains (losses) on financial instruments at fair value and foreign exchange |  | 84 |  | 63 |  | 78 |
Net investment losses related to other-than-temporary impairments |  | (5) |  | (13) |  | (15) |
Net gains (losses) on extinguishment of debt |  | 5 |  | (1) |  | 3 |
Other net realized gains (losses) |  | (282) |  | 17 |  | 28 |
Revenues of consolidated VIEs |  | 31 |  | 128 |  | 101 |
Inter-segment revenues |  | 0 |  | 0 |  | 0 |
Total revenues |  | 294 |  | 853 |  | 1,270 |
Losses and loss adjustment |  | 220 |  | 123 |  | 133 |
Operating |  | 177 |  | 190 |  | 239 |
Interest |  | 197 |  | 199 |  | 210 |
Expenses of consolidated VIEs |  | 39 |  | 52 |  | 47 |
Inter-segment expenses |  | 0 |  | 0 |  | 0 |
Total expenses |  | 633 |  | 564 |  | 629 |
Income (loss) before income taxes |  | (339) |  | 289 |  | 641 |
Provision (benefit) for income taxes |  | (1) |  | 109 |  | 72 |
Net income (loss) |  | (338) |  | 180 |  | 569 |
Identifiable assets |  | 11,137 |  | 14,836 |  | 16,263 |
U S Public Finance Insurance [Member] |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |
Losses and loss adjustment |  | 74 |  | 5 |  | (10) |
Operating Segments [Member] | U S Public Finance Insurance [Member] |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |
Revenues |  | 335 | [1] | 389 | [1] | 373 | [2]
Net change in fair value of insured derivatives |  |  |  |  |  | 1 |
Net gains (losses) on financial instruments at fair value and foreign exchange |  | 72 |  | 14 |  | 26 |
Net investment losses related to other-than-temporary impairments |  | (4) |  | (10) |  | (15) |
Other net realized gains (losses) |  | 2 |  | (4) |  | 14 |
Inter-segment revenues |  | 22 | [3] | 34 | [3] | 44 | [4]
Total revenues |  | 427 |  | 423 |  | 443 |
Losses and loss adjustment |  | 74 |  | 5 |  | (10) |
Operating |  | 40 |  | 38 |  | 38 |
Inter-segment expenses |  | 69 | [3] | 89 | [3] | 78 | [4]
Total expenses |  | 183 |  | 132 |  | 106 |
Income (loss) before income taxes |  | 244 |  | 291 |  | 337 |
Provision (benefit) for income taxes |  | 68 |  | 100 |  | 115 |
Net income (loss) |  | 176 |  | 191 |  | 222 |
Identifiable assets |  | 5,077 |  | 5,265 |  | 5,887 |
Operating Segments [Member] | Corporate Operations [Member] |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |
Revenues |  | 24 | [1] | 27 | [1] | 42 | [2]
Net gains (losses) on financial instruments at fair value and foreign exchange |  | (14) |  | 58 |  | 55 |
Net investment losses related to other-than-temporary impairments |  | (1) |  | (3) |  |  |
Net gains (losses) on extinguishment of debt |  | 5 |  | (1) |  | 3 |
Other net realized gains (losses) |  | (5) |  | 21 |  | 2 |
Revenues of consolidated VIEs |  |  |  |  |  | 0 |
Inter-segment revenues |  | 58 | [3] | 67 | [3] | 46 | [4]
Total revenues |  | 67 |  | 169 |  | 148 |
Operating |  | 80 |  | 79 |  | 87 |
Interest |  | 91 |  | 97 |  | 101 |
Inter-segment expenses |  | 4 | [3] | 7 | [3] | 15 | [4]
Total expenses |  | 175 |  | 183 |  | 203 |
Income (loss) before income taxes |  | (108) |  | (14) |  | (55) |
Provision (benefit) for income taxes |  | (15) |  | 7 |  | (173) |
Net income (loss) |  | (93) |  | (21) |  | 118 |
Identifiable assets |  | 2,479 |  | 2,599 |  | 2,838 |
Operating Segments [Member] | International And Structured Finance Insurance [Member] |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |
Revenues |  | 121 | [1] | 114 | [1] | 189 | [2]
Net change in fair value of insured derivatives |  | (19) |  | 129 |  | 458 |
Net gains (losses) on financial instruments at fair value and foreign exchange |  | 26 |  | (9) |  | 0 |
Other net realized gains (losses) |  | (279) |  |  |  | 12 |
Revenues of consolidated VIEs |  | 31 |  | 128 |  | 105 |
Inter-segment revenues |  | 51 | [3] | 63 | [3] | 55 | [4]
Total revenues |  | (69) |  | 425 |  | 819 |
Losses and loss adjustment |  | 146 |  | 118 |  | 143 |
Operating |  | 57 |  | 73 |  | 72 |
Interest |  | 106 |  | 102 |  | 109 |
Expenses of consolidated VIEs |  | 39 |  | 52 |  | 47 |
Inter-segment expenses |  | 52 | [3] | 64 | [3] | 64 | [4]
Total expenses |  | 400 |  | 409 |  | 435 |
Income (loss) before income taxes |  | (469) |  | 16 |  | 384 |
Provision (benefit) for income taxes |  | (52) |  | 3 |  | 134 |
Net income (loss) |  | (417) |  | 13 |  | 250 |
Identifiable assets |  | 6,486 |  | 9,870 |  | 10,073 |
Operating Segments [Member] | Advisory Services [Member] |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |
Revenues | [2] |  |  |  |  | 12 |
Net gains (losses) on financial instruments at fair value and foreign exchange |  |  |  |  |  | (3) |
Revenues of consolidated VIEs |  |  |  |  |  | (8) |
Inter-segment revenues | [4] |  |  |  |  | 22 |
Total revenues |  |  |  |  |  | 23 |
Operating |  |  |  |  |  | 42 |
Inter-segment expenses | [4] |  |  |  |  | 6 |
Total expenses |  |  |  |  |  | 48 |
Income (loss) before income taxes |  |  |  |  |  | (25) |
Provision (benefit) for income taxes |  |  |  |  |  | (6) |
Net income (loss) |  |  |  |  |  | (19) |
Identifiable assets |  |  |  |  |  | 793 |
Operating Segments [Member] | Conduit [Member] |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |
Revenues of consolidated VIEs |  |  |  |  |  | 4 |
Inter-segment revenues | [4] |  |  |  |  | (1) |
Total revenues |  |  |  |  |  | 3 |
Expenses of consolidated VIEs |  |  |  |  |  | 0 |
Inter-segment expenses | [4] |  |  |  |  | 9 |
Total expenses |  |  |  |  |  | 9 |
Income (loss) before income taxes |  |  |  |  |  | (6) |
Provision (benefit) for income taxes |  |  |  |  |  | 0 |
Net income (loss) |  |  |  |  |  | (6) |
Identifiable assets |  |  |  |  |  | 0 |
Intersegment Elimination [Member] |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |
Inter-segment revenues |  | (131) | [3] | (164) | [3] | (166) | [4]
Total revenues |  | (131) |  | (164) |  | (166) |
Inter-segment expenses |  | (125) | [3] | (160) | [3] | (172) | [4]
Total expenses |  | (125) |  | (160) |  | (172) |
Income (loss) before income taxes |  | (6) |  | (4) |  | 6 |
Provision (benefit) for income taxes |  | (2) |  | (1) |  | 2 |
Net income (loss) |  | (4) |  | (3) |  | 4 |
Identifiable assets |  | $ (2,905) | [5] | $ (2,898) | [5] | $ (3,328) | [6]
[1] | Represents the sum of third-party financial guarantee net premiums earned, net investment income, insurance-related fees and reimbursements and other fees.
[2] | Represents the sum of third-party financial guarantee net premiums earned, net investment income, insurance-related fees and reimbursements, investment management fees and other fees.
[3] | Represents intercompany premium income and expense and intercompany interest income and expense pertaining to intercompany receivables and payables.
[4] | Represents intercompany premium income and expense, intercompany asset management fees and expenses, intercompany interest income and expense pertaining to intercompany receivables and payables and intercompany loans.
[5] | Consists of intercompany deferred income taxes, reinsurance balances and repurchase agreements.
[6] | Consists of intercompany reinsurance balances, repurchase agreements and deferred income taxes.

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