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