Investments (Realized Investment Gains Losses, Net) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule of Gain (Loss) on Investments [Line Items]
Realized investment gains (losses), net	$ (2,681,320)	$ 884,073	$ (805,400)
Fixed maturities
Schedule of Gain (Loss) on Investments [Line Items]
Realized investment gains (losses), net	(3,931)	(83,731)	(3,177)
Commercial mortgage and other loans
Schedule of Gain (Loss) on Investments [Line Items]
Realized investment gains (losses), net	(753)	128	(840)
LPs/LLCs
Schedule of Gain (Loss) on Investments [Line Items]
Realized investment gains (losses), net	0	0	(39)
Derivatives
Schedule of Gain (Loss) on Investments [Line Items]
Realized investment gains (losses), net	(2,677,559)	967,503	(801,429)
Other invested assets
Schedule of Gain (Loss) on Investments [Line Items]
Realized investment gains (losses), net	164	123	0
Short-term investments and cash equivalents
Schedule of Gain (Loss) on Investments [Line Items]
Realized investment gains (losses), net	$ 759	$ 50	$ 85