Fair Value of Financial Instruments - Schedule of Unobservable Inputs Used for Level Three Fair Value Measurements of Financial Instruments on Recurring Basis (Detail) - USD ($)	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2016
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets, fair value	$ 2,357,000,000
Liabilities, fair value	3,257,000,000
Market Approach | Asset-backed securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets, fair value	396,000,000
Market Approach | Commercial mortgage-backed securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets, fair value	8,000,000
Market Approach | Corporates
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets, fair value	684,000,000
Market Approach | Municipals
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets, fair value	36,000,000
Market Approach | Foreign Government Debt Securities [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets, fair value	16,000,000
Market Approach | Residential mortgage-backed securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets, fair value	242,000,000
Third Parties [Member] | Asset-backed securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets, fair value	8,000,000
Black Scholes Model [Member] | Other invested assets
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets, fair value	$ 17,000,000
Fair value inputs, black scholes model	100.00%	100.00%
Matrix Pricing Valuation [Member] | Commercial mortgage-backed securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets, fair value		$ 39,000,000
Matrix Pricing Valuation [Member] | Corporates
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets, fair value	$ 524,000,000
Matrix Pricing Valuation [Member] | Hybrids
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets, fair value	9,000,000
Matrix Pricing Valuation [Member] | Residential mortgage-backed securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets, fair value	$ 333,000,000
Matrix Pricing Valuation [Member] | Funds withheld for reinsurance liabilities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs, black scholes model	100.00%	100.00%
Loan Recovery Valuation [Member] | Funds withheld for reinsurance liabilities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs, black scholes model		26.00%
Fixed indexed annuities | Income Approach Valuation Technique
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Liabilities, fair value	$ 2,551,000,000
Preferred shares reimbursement feature embedded derivative | Income Approach Valuation Technique
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Liabilities, fair value	22,000,000
Credit Spread	$ 0.0366	$ 0.0413
Yield Volatility	20.00%	20.00%
Minimum | Market Approach | Asset-backed securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs, quoted prices	97.12%	98.00%
Minimum | Market Approach | Commercial mortgage-backed securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs, quoted prices	100.44%	99.50%
Minimum | Market Approach | Corporates
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs, quoted prices	72.02%	73.55%
Minimum | Market Approach | Municipals
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs, quoted prices	108.82%	111.84%
Minimum | Market Approach | Foreign Government Debt Securities [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs, quoted prices	98.94%	104.16%
Minimum | Market Approach | Residential mortgage-backed securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs, quoted prices	92.09%	93.25%
Minimum | Third Parties [Member] | Asset-backed securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs, quoted prices	0.00%
Minimum | Black Scholes Model [Member] | Other invested assets
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs, black scholes model	7.20%
Minimum | Matrix Pricing Valuation [Member] | Commercial mortgage-backed securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs Matrix Pricing	102.12%
Minimum | Matrix Pricing Valuation [Member] | Corporates
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs Matrix Pricing	91.83%	67.72%
Minimum | Matrix Pricing Valuation [Member] | Hybrids
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs, quoted prices	94.99%	96.89%
Minimum | Matrix Pricing Valuation [Member] | Residential mortgage-backed securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs, quoted prices	99.98%
Minimum | Fixed indexed annuities | Income Approach Valuation Technique
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs, market value of option	0.00%	0.00%
Fair value inputs, swap rates	3.07%	2.24%
Fair value inputs, mortality multiplier	80.00%	80.00%
Fair value inputs, surrender rates	0.50%	0.50%
Fair value inputs, non performance spread	0.25%	0.25%
Fair Value Inputs Option Cost	0.11%	0.06%
Minimum | Fixed indexed annuities | Partial Withdrawls [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs Partial Withdrawals	1.00%	2.00%
Maximum | Market Approach | Asset-backed securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs, quoted prices	102.00%	102.56%
Maximum | Market Approach | Commercial mortgage-backed securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs, quoted prices	100.44%	122.78%
Maximum | Market Approach | Corporates
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs, quoted prices	105.50%	109.63%
Maximum | Market Approach | Municipals
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs, quoted prices	108.82%	111.84%
Maximum | Market Approach | Foreign Government Debt Securities [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs, quoted prices	99.83%	106.28%
Maximum | Market Approach | Residential mortgage-backed securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs, quoted prices	101.38%	102.25%
Maximum | Third Parties [Member] | Asset-backed securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs, quoted prices	99.70%
Maximum | Black Scholes Model [Member] | Other invested assets
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs, black scholes model	9.20%
Maximum | Matrix Pricing Valuation [Member] | Commercial mortgage-backed securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs Matrix Pricing	116.77%
Maximum | Matrix Pricing Valuation [Member] | Corporates
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs Matrix Pricing	110.13%	115.03%
Maximum | Matrix Pricing Valuation [Member] | Hybrids
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs, quoted prices	94.99%	96.89%
Maximum | Matrix Pricing Valuation [Member] | Residential mortgage-backed securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs, quoted prices	99.98%
Maximum | Fixed indexed annuities | Income Approach Valuation Technique
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs, market value of option	39.48%	29.93%
Fair value inputs, swap rates	3.12%	2.40%
Fair value inputs, mortality multiplier	80.00%	80.00%
Fair value inputs, surrender rates	75.00%	75.00%
Fair value inputs, non performance spread	0.25%	0.25%
Fair Value Inputs Option Cost	16.61%	17.33%
Maximum | Fixed indexed annuities | Partial Withdrawls [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs Partial Withdrawals	2.50%	3.50%
Weighted Average | Market Approach | Asset-backed securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs, quoted prices	99.40%	100.27%
Weighted Average | Market Approach | Commercial mortgage-backed securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs, quoted prices	100.44%	114.09%
Weighted Average | Market Approach | Corporates
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs, quoted prices	96.81%	99.77%
Weighted Average | Market Approach | Municipals
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs, quoted prices	108.82%	111.84%
Weighted Average | Market Approach | Foreign Government Debt Securities [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs, quoted prices	99.22%	104.82%
Weighted Average | Market Approach | Residential mortgage-backed securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs, quoted prices	99.68%	100.11%
Weighted Average | Third Parties [Member] | Asset-backed securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs, quoted prices	14.41%
Weighted Average | Matrix Pricing Valuation [Member] | Commercial mortgage-backed securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs Matrix Pricing	110.74%
Weighted Average | Matrix Pricing Valuation [Member] | Corporates
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs Matrix Pricing	99.14%	103.72%
Weighted Average | Matrix Pricing Valuation [Member] | Hybrids
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs, quoted prices	94.99%	96.89%
Weighted Average | Matrix Pricing Valuation [Member] | Residential mortgage-backed securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs, quoted prices	99.98%
Weighted Average | Fixed indexed annuities | Income Approach Valuation Technique
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs, market value of option	3.33%	4.11%
Fair value inputs, swap rates	3.09%	2.31%
Fair value inputs, mortality multiplier	80.00%	80.00%
Fair value inputs, surrender rates	5.96%	6.13%
Fair value inputs, non performance spread	0.25%	0.25%
Fair Value Inputs Option Cost	2.14%	1.99%
Weighted Average | Fixed indexed annuities | Partial Withdrawls [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Inputs Partial Withdrawals	2.00%	2.75%
Insurance Subsidiary | Income Approach Valuation Technique | Equity securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets, fair value	$ 4,000,000
Loan Participation - RadioShack (RSH) Corporation [Member] | Market Approach | Other invested assets
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Input Recovery Rate	7.11%	5.00%
Predecessor
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets, fair value		$ 1,785,000,000
Future Policy Benefit		728,000,000
Loan Recovery Value		1,000,000
Residential Mortage Backed securities		66,000,000
Liabilities, fair value		3,028,000,000
Predecessor | Market Approach | Asset-backed securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets, fair value		412,000,000
Predecessor | Market Approach | Commercial mortgage-backed securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets, fair value		49,000,000
Predecessor | Market Approach | Corporates
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets, fair value		763,000,000
Predecessor | Market Approach | Municipals
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets, fair value		38,000,000
Predecessor | Market Approach | Foreign Government Debt Securities [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets, fair value		17,000,000
Predecessor | Market Approach | Other invested assets
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Reinsurance Receivables, Funds Withheld			$ 3,000,000
Predecessor | Income Approach Valuation Technique | Corporates
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets, fair value		406,000,000
Predecessor | Income Approach Valuation Technique | Hybrids
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets, fair value		10,000,000
Predecessor | Fixed indexed annuities | Income Approach Valuation Technique
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Liabilities, fair value		2,277,000,000
Predecessor | Preferred shares reimbursement feature embedded derivative | Income Approach Valuation Technique
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Liabilities, fair value		23,000,000
Predecessor | Insurance Subsidiary | Market Approach | Equity securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets, fair value		3,000,000
Predecessor | Insurance Subsidiary | Market Approach | Other invested assets
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets, fair value		$ 17,000,000
FSRC [Member] | Minimum | Income Approach Valuation Technique | Future Policy Benefits, Nonperformance Risk Spread [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs, black scholes model	0.12%	0.27%
FSRC [Member] | Minimum | Income Approach Valuation Technique | Future Policy Benefits [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Risk Margin To Reflect Uncertainty	0.50%	0.54%
FSRC [Member] | Maximum | Income Approach Valuation Technique | Future Policy Benefits, Nonperformance Risk Spread [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs, black scholes model	0.15%
FSRC [Member] | Maximum | Income Approach Valuation Technique | Future Policy Benefits [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Risk Margin To Reflect Uncertainty	0.62%
FSRC [Member] | Weighted Average | Income Approach Valuation Technique | Future Policy Benefits, Nonperformance Risk Spread [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs, black scholes model	0.13%
FSRC [Member] | Weighted Average | Income Approach Valuation Technique | Future Policy Benefits [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Risk Margin To Reflect Uncertainty	0.54%