Investments (Maturities of Fixed Maturity Securities) (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Available-for-sale Securities, Debt Maturities [Abstract]
Amortized Cost, Due in one year or less	$ 15,378
Amortized Cost, Due after one year through five years	77,046
Amortized Cost, Due after five years through ten years	72,056
Amortized Cost, Due after ten years	118,055
Amortized Cost, Structured Securities	71,378
Amortized Cost, Subtotal	353,913	$ 332,964
Estimated Fair Value, Due in one year or less	15,464
Estimated Fair Value, Due after one year through five years	81,187
Estimated Fair Value, Due after five years through ten years	76,987
Estimated Fair Value, Due after ten years	143,470
Estimated Fair Value, Structured Securities	73,334
Available-for-sale Securities, Debt Securities	$ 390,442	$ 351,402