Certain Long-Duration Contracts with Guarantees Liabilities for Guarantee Benefits (Details) - Annuity Contracts - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Movement in Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross [Roll Forward]
Beginning balance	$ 12,526,898	$ 8,992,937	$ 8,797,230
Incurred guarantee benefits	5,637,113	3,562,205	286,847
Paid guarantee benefits	(73,138)	(54,895)	(70,802)
Change in unrealized investment gains and losses	36,986	26,651	(20,338)
Ending balance	18,127,859	12,526,898	8,992,937
GMDB
Movement in Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross [Roll Forward]
Beginning balance	681,504	638,403	622,802
Incurred guarantee benefits	139,032	68,142	103,596
Paid guarantee benefits	(68,693)	(51,418)	(67,887)
Change in unrealized investment gains and losses	36,612	26,377	(20,108)
Ending balance	788,455	681,504	638,403
GMAB/GMWB/ GMIWB
Movement in Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross [Roll Forward]
Beginning balance	11,822,998	8,332,474	8,151,902
Incurred guarantee benefits	5,491,006	3,490,524	180,572
Paid guarantee benefits	0	0	0
Change in unrealized investment gains and losses	0	0	0
Ending balance	17,314,004	11,822,998	8,332,474
GMIB
Movement in Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross [Roll Forward]
Beginning balance	22,396	22,060	22,526
Incurred guarantee benefits	7,075	3,539	2,679
Paid guarantee benefits	(4,445)	(3,477)	(2,915)
Change in unrealized investment gains and losses	374	274	(230)
Ending balance	$ 25,400	$ 22,396	$ 22,060