Certain Long-Duration Contracts with Guarantees (Variable Annuity Contracts) (Details) - Variable Annuity Contracts - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Return of net deposits | In the Event of Death
Net Amount at Risk by Product and Guarantee [Line Items]
Account value	$ 110,194,439	$ 34,305,352
Net amount at risk	$ 463,423	$ 341,707
Average attained age of contractholders	66 years	66 years
Minimum return or contract value | In the Event of Death
Net Amount at Risk by Product and Guarantee [Line Items]
Account value	$ 24,725,084	$ 6,976,880
Net amount at risk	$ 3,098,018	$ 1,194,988
Average attained age of contractholders	69 years	68 years
Minimum return or contract value | At Annuitization / Accumulation
Net Amount at Risk by Product and Guarantee [Line Items]
Account value	$ 120,237,955	$ 34,565,409
Net amount at risk	$ 5,041,214	$ 2,257,837
Average attained age of contractholders	66 years	66 years
Average period remaining until expected annuitization	0 years	0 years