Investments (Schedule of Credit Quality of Fixed Maturity Portfolio by NAIC Designation) (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Investment Holdings [Line Items]
Amortized cost	$ 37,059,450	$ 35,900,332
Fair value	39,932,345	36,487,216
NAIC, Class 1 Designation [Member]
Investment Holdings [Line Items]
Amortized cost	23,685,524	23,363,259
Fair value	25,965,937	24,207,801
NAIC, Class 2 Designation [Member]
Investment Holdings [Line Items]
Amortized cost	12,154,249	11,709,730
Fair value	12,860,194	11,589,325
NAIC, Class 3 Designation [Member]
Investment Holdings [Line Items]
Amortized cost	1,045,123	758,531
Fair value	972,142	643,293
NAIC, Class 4 Designation [Member]
Investment Holdings [Line Items]
Amortized cost	141,552	60,480
Fair value	107,753	44,312
NAIC, Class 5 Designation [Member]
Investment Holdings [Line Items]
Amortized cost	19,384	0
Fair value	12,180	0
NAIC, Class 6 Designation [Member]
Investment Holdings [Line Items]
Amortized cost	13,618	8,332
Fair value	$ 14,139	$ 2,485