Investments - Declines in Fair Value, Fixed Maturities (Details) $ in Millions	Sep. 30, 2015 USD ($)
Debt Securities [Member] | Investment Grade [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, One Year or Less, Fair Value	$ 2,233
Available For Sale Securities, Continuous Unrealized Loss Position, Twelve Months Or Longer, Fair Value	157
Available For Sale Securities, Continuous Unrealized Loss Position, One Year or Less, Amortized Cost	2,312
Available-for-sale Securities, Continuous Unrealized Loss Position, More Than One Year, Amortized Cost	169
Available-for-sale Securities, Continuous Unrealized Loss Position, One Year or Less, Accumulated Losses	(79)
Available-for-sale Securities, Continuous Unrealized Loss Position, More Than One Year, Accumulated Losses	$ (12)
Debt Securities [Member] | Investment Grade [Member] | One Year Or Less [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	417
Debt Securities [Member] | Investment Grade [Member] | More Than One Year [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	60
Debt Securities [Member] | Below Investment Grade [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, One Year or Less, Fair Value	$ 479
Available For Sale Securities, Continuous Unrealized Loss Position, Twelve Months Or Longer, Fair Value	105
Available For Sale Securities, Continuous Unrealized Loss Position, One Year or Less, Amortized Cost	509
Available-for-sale Securities, Continuous Unrealized Loss Position, More Than One Year, Amortized Cost	123
Available-for-sale Securities, Continuous Unrealized Loss Position, One Year or Less, Accumulated Losses	(30)
Available-for-sale Securities, Continuous Unrealized Loss Position, More Than One Year, Accumulated Losses	$ (18)
Debt Securities [Member] | Below Investment Grade [Member] | One Year Or Less [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	224
Debt Securities [Member] | Below Investment Grade [Member] | More Than One Year [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	34
Equity securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Securities with a significant unrealized loss reflected in accumulated other comprehensive income	$ 0