Investments (Realized Investment Gains Losses Net) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	$ (3,442,760)	$ 6,052	$ 7,368
Fixed maturities
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	86,184	4,831	14,706
Equity securities
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	0	0	1
Commercial mortgage and other loans
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	(2,326)	(161)	774
Derivatives
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	(3,526,514)	1,381	(8,113)
Other long-term investments
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	(648)	1	0
Short-term investments
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	$ 544	$ 0	$ 0