Income Taxes (Components of Income Tax Expense (Benefit)) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current tax expense (benefit):
U.S. federal	$ (422,999)	$ 501,088	$ 2,524,458
State and local	0	1,349	0
Total	(422,999)	502,437	2,524,458
Deferred tax expense (benefit):
U.S. federal	584,503	698,662	(3,204,951)
State and local	0	0	0
Total	584,503	698,662	(3,204,951)
Total income tax expense (benefit)	161,504	1,201,099	(680,493)
Total income tax expense (benefit) reported in equity related to:
Other comprehensive income (loss)	(52,510)	98,644	(194,446)
Additional paid-in capital	0	0	(9,531)
Total income tax expense (benefit)	$ 108,994	$ 1,299,743	$ (884,470)