Income Taxes (Reconciliation To Effective Rate) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Expected federal income tax expense (benefit)	$ 391,158	$ (619,704)	$ 57,727
Non-taxable investment income	(46,625)	(49,630)	(56,614)
Tax credits	(10,358)	(10,507)	(9,389)
Changes in tax law	882,175	0	0
Other	(15,251)	(652)	(9)
Total income tax expense (benefit)	$ 1,201,099	$ (680,493)	$ (8,285)
Effective tax rate	107.50%	38.40%	(5.00%)