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, 2016	Dec. 31, 2015
Variable Annuity Contracts | Return of net deposits | In the Event of Death(2)
Net Amount at Risk by Product and Guarantee [Line Items]
Account value	$ 85,056,405	$ 79,034,807
Net amount at risk	$ 178,806	$ 385,773
Average attained age of contractholders	64 years	64 years
Variable Annuity Contracts | Minimum return or contract value | In the Event of Death(2)
Net Amount at Risk by Product and Guarantee [Line Items]
Account value	$ 20,091,528	$ 20,113,504
Net amount at risk	$ 2,039,249	$ 2,349,232
Average attained age of contractholders	68 years	68 years
Variable Annuity Contracts | Minimum return or contract value | At Annuitization / Accumulation
Net Amount at Risk by Product and Guarantee [Line Items]
Account value	$ 95,908,923	$ 89,935,139
Net amount at risk	$ 2,875,524	$ 2,633,207
Average attained age of contractholders	65 years	64 years
Average period remaining until earliest expected annuitization	0 years	0 years
Variable Life, Variable Universal Life and Universal Life Contracts | No-lapse guarantees | In the Event of Death(2)
Net Amount at Risk by Product and Guarantee [Line Items]
Separate account value	$ 3,125,804	$ 2,907,924
General account value	6,234,678	5,449,616
Net amount at risk	$ 119,838,053	$ 103,714,953
Average attained age of contractholders	55 years	54 years