Certain Long-Duration Contracts with Guarantees Liabilities for Guarantee Benefits (Details) - Annuity Contracts - 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	$ 8,992,937	$ 8,797,230	$ 8,382,545
Incurred guarantee benefits	3,562,205	286,847	462,488
Paid guarantee benefits	(54,895)	(70,802)	(60,851)
Change in unrealized investment gains and losses	26,651	(20,338)	13,048
Ending balance	12,526,898	8,992,937	8,797,230
GMDB
Movement in Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross [Roll Forward]
Beginning balance	638,403	622,802	637,319
Incurred guarantee benefits	68,142	103,596	29,605
Paid guarantee benefits	(51,418)	(67,887)	(57,053)
Change in unrealized investment gains and losses	26,377	(20,108)	12,931
Ending balance	681,504	638,403	622,802
GMAB/GMWB/ GMIWB
Movement in Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross [Roll Forward]
Beginning balance	8,332,474	8,151,902	7,707,333
Incurred guarantee benefits	3,490,524	180,572	444,569
Paid guarantee benefits	0	0	0
Change in unrealized investment gains and losses	0	0	0
Ending balance	11,822,998	8,332,474	8,151,902
GMIB
Movement in Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross [Roll Forward]
Beginning balance	22,060	22,526	37,893
Incurred guarantee benefits	3,539	2,679	(11,686)
Paid guarantee benefits	(3,477)	(2,915)	(3,798)
Change in unrealized investment gains and losses	274	(230)	117
Ending balance	$ 22,396	$ 22,060	$ 22,526