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Fair Value Measurements - Information about Valuation Inputs for Fixed Income Securities Classified as Level 3 (Detail) - Successor [Member] - USD ($) $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |  |  |
Other Investments | $ 431,630 | $ 450,307 |  |
Available-for-sale Securities | $ 5,309,161 | $ 6,049,908 |  |
Ambac insured Re-remic [Member] |  |  |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |  |  |
Coupon rate | 2.05% |  |  |
Fair Value Inputs Maturity | 7 months 24 days |  |  |
Yield | 0.00% |  |  |
Asset-backed Securities [Member] |  |  |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |  |  |
Coupon rate | 5.97% | 5.93% |  |
Fair Value Inputs Maturity | 17 years 9 days | 17 years 8 months 25 days |  |
Yield | 12.00% | 13.50% |  |
Fair Value, Inputs, Level 3 [Member] |  |  |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |  |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability | $ 12,561,185 | $ 11,369,112 | $ 11,497,098 | $ 13,845,454
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings | 782,597 | 870,935 | (545,308) |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss | 1,010,012 | (1,892,948) | (739,919) |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases | 35,781 | 99,018 | 359,193 |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales | (79,319) | 0 | 0 |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements | (604,766) | (51,254) | (344,865) |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Into Level Three | 47,768 | 108,365 | (752,334) |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Out Of Level Three | 0 | 737,898 | 0 |
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held | 662,293 | 815,358 | (607,235) |
Fair Value, Inputs, Level 3 [Member] | Ambac insured Re-remic [Member] |  |  |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |  |  |
Available-for-sale Securities |  | 0 |  |
Fair Value, Inputs, Level 3 [Member] | Corporate Obligations [Member] |  |  |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |  |  |
Available-for-sale Securities | 0 | 0 |  |
Fair Value, Inputs, Level 3 [Member] | Residential Mortgage-Backed Securities [Member] |  |  |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |  |  |
Available-for-sale Securities | 736,017 | 696,713 |  |
Fair Value, Inputs, Level 3 [Member] | RMBS Priced Using Discounted Cash Flow Approach [Member] |  |  |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |  |  |
Available-for-sale Securities | 26,067 |  |  |
Fair Value, Inputs, Level 3 [Member] | Asset-backed Securities [Member] |  |  |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |  |  |
Available-for-sale Securities | $ 72,540 | $ 65,990 |  |
Variable Interest Entity, Primary Beneficiary [Member] |  |  |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |  |  |
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held |  |  | $ (579,620) |
Variable Interest Entity, Primary Beneficiary [Member] | United States Transactions [Member] |  |  |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |  |  |
Coupon rate | 5.88% |  |  |
Fair Value Inputs Maturity | 20 years 8 months 68 days |  |  |
Yield | 5.86% |  |  |
Variable Interest Entity, Primary Beneficiary [Member] | European Transactions [Member] |  |  |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |  |  |
Coupon rate |  | 0.40% | 0.46% |
Fair Value Inputs Maturity |  | 15 years 3 months 11 days | 16 years 1 month 28 days |
Yield |  | 4.82% | 4.95% |
Variable Interest Entity, Primary Beneficiary [Member] | Fair Value, Inputs, Level 3 [Member] | Corporate Obligations [Member] |  |  |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |  |  |
Available-for-sale Securities | $ 2,914,145 | $ 2,622,566 |  |
Real Estate [Member] |  |  |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |  |  |
Other Investments | 33,154 | 33,303 |  |
Hedge Funds, Multi-strategy [Member] |  |  |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |  |  |
Other Investments | 53,054 | 53,985 |  |
Interest Rate Contract [Member] |  |  |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |  |  |
Other Investments | 136,603 | 261,315 |  |
Illiquid Investments [Member] |  |  |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |  |  |
Other Investments | $ 67,787 | $ 39,068 |  |

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