Investments - Declines in Fair Value, Fixed Maturities (Details) - Jun. 30, 2015 $ in Millions	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	$ 2,722
Available For Sale Securities, Continuous Unrealized Loss Position, Twelve Months Or Longer, Fair Value	158
Available For Sale Securities, Continuous Unrealized Loss Position, One Year or Less, Amortized Cost	2,786
Available-for-sale Securities, Continuous Unrealized Loss Position, More Than One Year, Amortized Cost	166
Available-for-sale Securities, Continuous Unrealized Loss Position, One Year or Less, Accumulated Losses	(64)
Available-for-sale Securities, Continuous Unrealized Loss Position, More Than One Year, Accumulated Losses	$ (8)
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	515
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	70
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	$ 400
Available For Sale Securities, Continuous Unrealized Loss Position, Twelve Months Or Longer, Fair Value	90
Available For Sale Securities, Continuous Unrealized Loss Position, One Year or Less, Amortized Cost	420
Available-for-sale Securities, Continuous Unrealized Loss Position, More Than One Year, Amortized Cost	104
Available-for-sale Securities, Continuous Unrealized Loss Position, One Year or Less, Accumulated Losses	(20)
Available-for-sale Securities, Continuous Unrealized Loss Position, More Than One Year, Accumulated Losses	$ (14)
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	207
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	28
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