Certain Long-Duration Contracts with Guarantees (Liabilities for Guarantee Benefits) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Movement in Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross [Roll Forward]
Beginning balance	$ 11,249,071	$ 10,857,362	$ 9,514,220
Incurred guarantee benefits	4,469,472	927,056	1,228,755
Paid guarantee benefits	(138,843)	(114,776)	(41,961)
Change in unrealized investment gains and losses	827,707	(420,571)	156,348
Ending balance	16,407,407	11,249,071	10,857,362
GMDB | Annuity Contracts
Movement in Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross [Roll Forward]
Beginning balance	411,568	390,338	387,993
Incurred guarantee benefits	52,717	71,467	16,999
Paid guarantee benefits	(25,992)	(35,800)	(25,942)
Change in unrealized investment gains and losses	22,208	(14,437)	11,288
Ending balance	460,501	411,568	390,338
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	5,231,854	4,997,310	4,058,181
Incurred guarantee benefits	1,473,762	717,444	808,834
Paid guarantee benefits	(110,642)	(76,944)	(14,642)
Change in unrealized investment gains and losses	805,259	(405,956)	144,937
Ending balance	7,400,233	5,231,854	4,997,310
GMIB | Annuity Contracts
Movement in Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross [Roll Forward]
Beginning balance	16,810	17,131	27,038
Incurred guarantee benefits	2,266	1,889	(8,653)
Paid guarantee benefits	(2,209)	(2,032)	(1,377)
Change in unrealized investment gains and losses	240	(178)	123
Ending balance	17,107	16,810	17,131
GMWB/GMIWB/ GMAB | Annuity Contracts
Movement in Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross [Roll Forward]
Beginning balance	5,588,839	5,452,583	5,041,008
Incurred guarantee benefits	2,940,727	136,256	411,575
Paid guarantee benefits	0	0	0
Change in unrealized investment gains and losses	0	0	0
Ending balance	$ 8,529,566	$ 5,588,839	$ 5,452,583