Certain Long-Duration Contracts with Guarantees (Liabilities for Guarantee Benefits) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Movement in Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross [Roll Forward]
Beginning balance	$ 10,857,362	$ 9,514,220	$ 8,858,768
Incurred guarantee benefits	927,056	1,228,755	628,842
Paid guarantee benefits	(114,776)	(41,961)	(76,447)
Change in unrealized investment gains and losses	(420,571)	156,348	103,057
Ending balance	11,249,071	10,857,362	9,514,220
GMDB | Annuity Contracts
Movement in Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross [Roll Forward]
Beginning balance	390,338	387,993	376,894
Incurred guarantee benefits	71,467	16,999	48,832
Paid guarantee benefits	(35,800)	(25,942)	(38,661)
Change in unrealized investment gains and losses	(14,437)	11,288	928
Ending balance	411,568	390,338	387,993
GMDB | Variable Life, Variable Universal Life & Universal Life
Movement in Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross [Roll Forward]
Beginning balance	4,997,310	4,058,181	3,245,821
Incurred guarantee benefits	717,444	808,834	746,130
Paid guarantee benefits	(76,944)	(14,642)	(35,894)
Change in unrealized investment gains and losses	(405,956)	144,937	102,124
Ending balance	5,231,854	4,997,310	4,058,181
GMIB | Annuity Contracts
Movement in Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross [Roll Forward]
Beginning balance	17,131	27,038	30,618
Incurred guarantee benefits	1,889	(8,653)	(1,693)
Paid guarantee benefits	(2,032)	(1,377)	(1,892)
Change in unrealized investment gains and losses	(178)	123	5
Ending balance	16,810	17,131	27,038
GMWB/GMIWB/ GMAB | Annuity Contracts
Movement in Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross [Roll Forward]
Beginning balance	5,452,583	5,041,008	5,205,435
Incurred guarantee benefits	136,256	411,575	(164,427)
Paid guarantee benefits	0	0	0
Change in unrealized investment gains and losses	0	0	0
Ending balance	$ 5,588,839	$ 5,452,583	$ 5,041,008