Certain Long-Duration Contracts with Guarantees (Variable Annuity Contracts) (Details) - Annuity Contracts - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Return of net deposits | In the Event of Death
Net Amount at Risk by Product and Guarantee [Line Items]
Account value	$ 120,240,930	$ 106,779,202
Net amount at risk	$ 229,080	$ 843,419
Average attained age of contractholders	68 years	67 years
Minimum return or contract value | In the Event of Death
Net Amount at Risk by Product and Guarantee [Line Items]
Account value	$ 23,563,604	$ 22,184,537
Net amount at risk	$ 2,254,621	$ 4,322,406
Average attained age of contractholders	70 years	70 years
Minimum return or contract value | At Annuitization / Accumulation
Net Amount at Risk by Product and Guarantee [Line Items]
Account value	$ 129,812,105	$ 115,822,894
Net amount at risk	$ 3,989,437	$ 7,252,486
Average attained age of contractholders	69 years	68 years
Average period remaining until earliest expected annuitization	0 years	0 years