Investments (Amortized Cost And Fair Value Of Fixed Maturity Securities, By Contractual Maturity) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Amortized Cost
Available For Sale Securities, Amortized Cost	$ 18,951.8	$ 18,478.5
Fair Value
Available for sale securities Fair Value	19,909.9us-gaap_AvailableForSaleSecurities	19,254.9us-gaap_AvailableForSaleSecurities
Fixed Maturity Securities [Member]
Amortized Cost
Due in one year or less, Amortized Cost	507.3
Due after one year through five years, Amortized Cost	4,649.6
Due after five years through ten years, Amortized Cost	5,227.9
Due after ten years, Amortized Cost	4,631.8
Mortgage-backed securities, Amortized Cost	2,604.5
Available For Sale Securities, Amortized Cost	17,621.1	17,282.6
Fair Value
Due in one year or less, Estimated Fair Value	510.8
Due after one year through five years, Estimated Fair Value	4,702.9
Due after five years through ten years, Estimated Fair Value	5,360.8
Due after ten years, Estimated Fair Value	4,728.4
Mortgage-backed securities, Estimated Fair Value	2,668.9
Available for sale securities Fair Value	$ 17,971.8	$ 17,488.1

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Amount of available-for-sale debt securities at cost, net of adjustments, maturing in the sixth fiscal year through the tenth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings (less any cumulative-effect adjustments, as defined) and fair value hedge accounting adjustments.

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Amount of available-for-sale debt securities at fair value maturing in the sixth fiscal year through the tenth fiscal year following the latest fiscal year.

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Amount of available-for-sale debt securities at cost, net of adjustments, maturing in the second fiscal year through the fifth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings (less any cumulative-effect adjustments, as defined) and fair value hedge accounting adjustments.

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Amount of available-for-sale debt securities at fair value maturing in the second fiscal year through the fifth fiscal year following the latest fiscal year.

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Amount of available-for-sale debt securities at cost, net of adjustments, maturing after the tenth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings (less any cumulative-effect adjustments, as defined) and fair value hedge accounting adjustments.

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Amount of available-for-sale debt securities at fair value maturing after the tenth fiscal year following the latest fiscal year.

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Amount of available-for-sale debt securities at cost, net of adjustments, maturing in the next fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings (less any cumulative-effect adjustments, as defined) and fair value hedge accounting adjustments.

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Amount of available-for-sale debt securities at fair value maturing in the next fiscal year following the latest fiscal year.

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