Fair Value of Assets and Liabilities (Quantitative Info for Level 3 Inputs) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Corporate securities	$ 74,271	$ 63,647
Future policy benefits	26,612,760	12,932,461
Policyholders’ account balances	6,596,004	6,180,359
Fair Value, Measurements, Recurring
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Future policy benefits	25,302,654	11,822,998
Policyholders’ account balances	$ 158,920	196,892
Level 3 | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Policyholder Age	45 years
Level 3 | Minimum | Future policy benefits
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Mortality rate	0.00%
Level 3 | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Policyholder Age	90 years
Level 3 | Fair Value, Measurements, Recurring
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Future policy benefits	$ 25,302,654	11,822,998
Policyholders’ account balances	$ 158,920	$ 196,892
Level 3 | Internal | Minimum | Discounted cash flow | Future policy benefits
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Lapse rate	1.00%	1.00%
Spread over LIBOR	1.40%	0.10%
Utilization rate	43.00%	43.00%
Withdrawal rate (greater than maximum range)	78.00%	78.00%
Mortality rate	0.00%	0.00%
Equity volatility curve	18.00%	13.00%
Level 3 | Internal | Minimum | Discounted cash flow | Policyholders' account balances
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Lapse rate	1.00%	1.00%
Spread over LIBOR	1.40%	0.10%
Equity volatility curve	6.00%	6.00%
Level 3 | Internal | Minimum | Discounted cash flow | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Discount rate	1.90%	4.79%
Level 3 | Internal | Minimum | Market comparables | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
EBITDA multiples	6.7	6.7
Level 3 | Internal | Maximum | Discounted cash flow | Future policy benefits
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Lapse rate	18.00%	18.00%
Spread over LIBOR	2.02%	1.23%
Utilization rate	97.00%	97.00%
Withdrawal rate (greater than maximum range)	100.00%	100.00%
Mortality rate	15.00%	15.00%
Equity volatility curve	33.00%	23.00%
Level 3 | Internal | Maximum | Discounted cash flow | Policyholders' account balances
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Lapse rate	42.00%	42.00%
Spread over LIBOR	2.02%	1.23%
Equity volatility curve	53.00%	25.00%
Level 3 | Internal | Maximum | Discounted cash flow | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Discount rate	25.00%	20.00%
Level 3 | Internal | Maximum | Market comparables | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
EBITDA multiples	6.7	6.7
Level 3 | Internal | Weighted Average | Discounted cash flow | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Discount rate	7.98%	8.66%
Level 3 | Internal | Weighted Average | Market comparables | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
EBITDA multiples	6.7	6.7
Level 3 | Internal | Fair Value, Measurements, Recurring | Future policy benefits
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Future policy benefits	$ 25,302,654	$ 11,822,998
Level 3 | Internal | Fair Value, Measurements, Recurring | Policyholders' account balances
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Policyholders’ account balances	158,920	196,892
Level 3 | Internal | Fair Value, Measurements, Recurring | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Corporate securities	30,390	17,149
Level 3 | Internal | Fair Value, Measurements, Recurring | Reinsurance recoverables
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Reinsurance recoverables	$ 565,090	$ 302,814