Investments (Schedule of Credit Quality of Fixed Maturity Portfolio by NAIC Designation) (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Investment Holdings [Line Items]
Amortized cost	$ 34,134,904	$ 30,281,478
Fair value	35,451,842	32,521,040
NAIC, Class 1 Designation [Member]
Investment Holdings [Line Items]
Amortized cost	21,918,272	19,223,151
Fair value	23,171,086	20,941,634
NAIC, Class 2 Designation [Member]
Investment Holdings [Line Items]
Amortized cost	11,432,147	10,432,593
Fair value	11,581,162	10,981,618
NAIC, Class 3 Designation [Member]
Investment Holdings [Line Items]
Amortized cost	745,289	602,191
Fair value	679,289	583,313
NAIC, Class 4 Designation [Member]
Investment Holdings [Line Items]
Amortized cost	31,042	22,888
Fair value	17,256	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	8,154	655
Fair value	$ 3,049	$ 386