Fair Value of Assets and Liabilities (Quantitative Info for Level 3 Inputs) (Details) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2020		Dec. 31, 2019
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Corporate securities	$ 6,208		$ 6,360
Future policy benefits	35,511,798	[1]	25,258,673
Fair Value, Measurements, Recurring
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Future policy benefits	16,661,255		8,529,566
Policyholders’ account balances	$ 1,076,904		962,351
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	$ 16,661,255		8,529,566
Policyholders’ account balances	$ 1,076,904		$ 962,351
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	0.09%		0.10%
Utilization rate	39.00%		43.00%
Withdrawal rate (greater than maximum range)	76.00%		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	0.09%		0.10%
Mortality rate	0.00%		0.00%
Equity volatility curve	19.00%		10.00%
Level 3 | Internal | Minimum   | Discounted cash flow | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Discount Rate	1.30%		5.24%
Level 3 | Internal | Minimum   | Market comparables | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
EBITDA			5.7
Level 3 | Internal | Maximum | Discounted cash flow | Future policy benefits
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Lapse rate	20.00%		18.00%
Spread over LIBOR	1.59%		1.23%
Utilization rate	96.00%		97.00%
Withdrawal rate (greater than maximum range)	100.00%		100.00%
Mortality rate	15.00%		15.00%
Equity volatility curve	26.00%		23.00%
Level 3 | Internal | Maximum | Discounted cash flow | Policyholders' account balances
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Lapse rate	6.00%		6.00%
Spread over LIBOR	1.59%		1.23%
Mortality rate	24.00%		24.00%
Equity volatility curve	35.00%		23.00%
Level 3 | Internal | Maximum | Discounted cash flow | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Discount Rate	12.33%		17.47%
Level 3 | Internal | Maximum | Market comparables | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
EBITDA			5.7
Level 3 | Internal | Weighted Average | Discounted cash flow | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Discount Rate	3.68%		8.25%
Level 3 | Internal | Weighted Average | Market comparables | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
EBITDA			5.7
Level 3 | Internal | Fair Value, Measurements, Recurring | Future policy benefits
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Future policy benefits	$ 16,661,255		$ 8,529,566
Level 3 | Internal | Fair Value, Measurements, Recurring | Policyholders' account balances
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Policyholders’ account balances	1,076,904		962,351
Level 3 | Internal | Fair Value, Measurements, Recurring | Corporate securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Corporate securities	137,857		27,816
Level 3 | Internal | Fair Value, Measurements, Recurring | Reinsurance recoverables
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Reinsurance recoverables	$ 16,675,343		$ 8,539,671

[1] September 30, 2020 amounts include the impacts of the January 1, 2020 adoption of ASU 2016-13. See Note 2 for details.