Investments (Credit Quality of Fixed Maturity Security Portfolio by NAIC Designation) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Investment Holdings [Line Items]
Amortized cost	$ 35,900,332	$ 30,281,478
Fair value	36,487,216	32,521,040
NAIC, Class 1 Designation [Member]
Investment Holdings [Line Items]
Amortized cost	23,363,259	19,223,151
Fair value	24,207,801	20,941,634
NAIC, Class 2 Designation [Member]
Investment Holdings [Line Items]
Amortized cost	11,709,730	10,432,593
Fair value	11,589,325	10,981,618
NAIC, Class 3 Designation [Member]
Investment Holdings [Line Items]
Amortized cost	758,531	602,191
Fair value	643,293	583,313
NAIC, Class 4 Designation [Member]
Investment Holdings [Line Items]
Amortized cost	60,480	22,888
Fair value	44,312	14,089
NAIC, Class 5 Designation [Member]
Investment Holdings [Line Items]
Amortized cost	0	0
Fair value	0	0
NAIC, Class 6 Designation [Member]
Investment Holdings [Line Items]
Amortized cost	8,332	655
Fair value	$ 2,485	$ 386