Fair Value Measurements - Significant Unobservable Inputs (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Actuarial Assumptions, Lapses, threshold percentage	85.00%	85.00%
Actuarial Assumptions, Policyholder Deposits, threshold percentage	85.00%	85.00%
Fixed indexed annuities (FIA) | Derivative Financial Instruments, Liabilities | Market Approach Valuation Technique | Minimum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Interest rate implied volatility	0.00%	0.00%
Actuarial Assumptions, Policyholder Deposits	0.00%	0.00%
Fixed indexed annuities (FIA) | Derivative Financial Instruments, Liabilities | Market Approach Valuation Technique | Maximum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Interest rate implied volatility	0.00%	0.00%
Actuarial Assumptions, Policyholder Deposits	0.00%	0.00%
Fixed indexed annuities (FIA) | Investment Contract | Market Approach Valuation Technique | Minimum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Nonperformance risk	0.38%	0.02%
Actuarial Assumptions, Lapses	0.00%	0.00%
Fair Value Input, Actual Assumption, Partial Withdrawal	0.00%	0.50%
Fixed indexed annuities (FIA) | Investment Contract | Market Approach Valuation Technique | Maximum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Nonperformance risk	1.20%	1.10%
Actuarial Assumptions, Lapses	42.00%	42.00%
Fair Value Input, Actual Assumption, Partial Withdrawal	7.00%	7.00%
Stabilizer / MCG
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Percentage of Plans	100.00%	100.00%
Stabilizer / MCG | Derivative Financial Instruments, Liabilities | Market Approach Valuation Technique | Minimum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Interest rate implied volatility	0.10%	0.10%
Nonperformance risk	0.38%	0.02%
Actuarial Assumptions, Lapses	0.00%	0.00%
Actuarial Assumptions, Policyholder Deposits	0.00%	0.00%
Actuarial Assumptions, Lapses under percent threshold	0.00%	0.00%
Actuarial Assumptions, Policyholder Deposits under percent threshold	0.00%	0.00%
Fair Value Input, Actual Assumption, Partial Withdrawal	0.00%	0.00%
Stabilizer / MCG | Derivative Financial Instruments, Liabilities | Market Approach Valuation Technique | Maximum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Interest rate implied volatility	6.50%	6.30%
Nonperformance risk	1.20%	1.10%
Actuarial Assumptions, Lapses	50.00%	50.00%
Actuarial Assumptions, Policyholder Deposits	50.00%	50.00%
Actuarial Assumptions, Lapses under percent threshold	30.00%	30.00%
Actuarial Assumptions, Policyholder Deposits under percent threshold	25.00%	25.00%
Fair Value Input, Actual Assumption, Partial Withdrawal	0.00%	0.00%
Stabilizer (Investment Only) and MCG Contracts
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Percentage of Plans	92.00%	92.00%
Stabilizer (Investment Only) and MCG Contracts | Derivative Financial Instruments, Liabilities | Market Approach Valuation Technique | Minimum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Actuarial Assumptions, Lapses	0.00%	0.00%
Actuarial Assumptions, Policyholder Deposits	0.00%	0.00%
Actuarial Assumptions, Lapses under percent threshold	0.00%	0.00%
Actuarial Assumptions, Policyholder Deposits under percent threshold	0.00%	0.00%
Stabilizer (Investment Only) and MCG Contracts | Derivative Financial Instruments, Liabilities | Market Approach Valuation Technique | Maximum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Actuarial Assumptions, Lapses	25.00%	25.00%
Actuarial Assumptions, Policyholder Deposits	30.00%	30.00%
Actuarial Assumptions, Lapses under percent threshold	15.00%	15.00%
Actuarial Assumptions, Policyholder Deposits under percent threshold	15.00%	15.00%
Stabilizer with Recordkeeping Agreements
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Percentage of Plans	8.00%	8.00%
Stabilizer with Recordkeeping Agreements | Derivative Financial Instruments, Liabilities | Market Approach Valuation Technique | Minimum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Actuarial Assumptions, Lapses	0.00%	0.00%
Actuarial Assumptions, Policyholder Deposits	0.00%	0.00%
Actuarial Assumptions, Lapses under percent threshold	0.00%	0.00%
Actuarial Assumptions, Policyholder Deposits under percent threshold	0.00%	0.00%
Stabilizer with Recordkeeping Agreements | Derivative Financial Instruments, Liabilities | Market Approach Valuation Technique | Maximum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Actuarial Assumptions, Lapses	50.00%	50.00%
Actuarial Assumptions, Policyholder Deposits	50.00%	50.00%
Actuarial Assumptions, Lapses under percent threshold	30.00%	30.00%
Actuarial Assumptions, Policyholder Deposits under percent threshold	25.00%	25.00%