Investments - Declines in Fair Value, Fixed Maturities (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014
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	$ 999
Available-for-sale Securities, Continuous Unrealized Loss Position, More Than One Year, Fair Value	256
Available For Sale Securities, Continuous Unrealized Loss Position, One Year or Less, Amortized Cost	1,010
Available-for-sale Securities, Continuous Unrealized Loss Position, More Than One Year, Amortized Cost	264
Available-for-sale Securities, Continuous Unrealized Loss Position, One Year or Less, Aggregate Losses	(11)
Available-for-sale Securities, Continuous Unrealized Loss Position, More Than One Year, Aggregate 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	251
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	93
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	293
Available-for-sale Securities, Continuous Unrealized Loss Position, More Than One Year, Fair Value	78
Available For Sale Securities, Continuous Unrealized Loss Position, One Year or Less, Amortized Cost	307
Available-for-sale Securities, Continuous Unrealized Loss Position, More Than One Year, Amortized Cost	87
Available-for-sale Securities, Continuous Unrealized Loss Position, One Year or Less, Aggregate Losses	(14)
Available-for-sale Securities, Continuous Unrealized Loss Position, More Than One Year, Aggregate Losses	(9)
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	236
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	22
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