Certain Long-Duration Contracts with Guarantees (Variable Annuity, Variable Life, Variable Universal Life and Universal Life Contracts) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Annuity Contracts | Return of net deposits | In the Event of Death
Net Amount at Risk by Product and Guarantee [Line Items]
Account value	$ 87,412,536	$ 94,605,484
Net amount at risk	$ 656,027	$ 23,143
Average attained age of contractholders	66 years	65 years
Annuity Contracts | Minimum return or contract value | In the Event of Death
Net Amount at Risk by Product and Guarantee [Line Items]
Account value	$ 18,574,416	$ 21,331,358
Net amount at risk	$ 3,186,237	$ 1,309,080
Average attained age of contractholders	70 years	69 years
Annuity Contracts | Minimum return or contract value | At Annuitization / Accumulation
Net Amount at Risk by Product and Guarantee [Line Items]
Account value	$ 97,055,710	$ 105,887,964
Net amount at risk	$ 4,510,250	$ 1,729,783
Average attained age of contractholders	67 years	66 years
Average period remaining until earliest expected annuitization	0 years	0 years
Variable Life, Variable Universal Life and Universal Life Contracts
Net Amount at Risk by Product and Guarantee [Line Items]
Separate account value	$ 3,301,084	$ 3,496,913
Variable Life, Variable Universal Life and Universal Life Contracts | In the Event of Death
Net Amount at Risk by Product and Guarantee [Line Items]
General account value	8,224,464	7,209,522
Net amount at risk	$ 144,225,578	$ 135,077,843
Average attained age of contractholders	55 years	55 years