Investment Securities (Net Realized and Unrealized Investement Gains and Losses) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Investments, Debt and Equity Securities [Abstract]
Net realized investment gains, pre-tax	$ 233.8	$ 104.5	$ 68.1
Net unrealized investment gains, pre-tax	50.1	57.2	50.1
Net realized and unrealized investment gains, pre-tax	283.9	161.7	118.2
Income tax expense attributable to net realized and unrealized investment gains	(69.7)	(21.9)	(26.8)
Net realized and unrealized investment gains, after tax	$ 214.2	$ 139.8	$ 91.4

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- Definition

The sum of the realized and unrealized net gain (loss) on trading securities during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Trading Securities

-URI http://asc.fasb.org/extlink&oid=6526789

+ Details

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- Definition

Net Realized and Unrealized Gain (Loss) on Trading Securities, Net of Tax

+ References

No definition available.

+ Details

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- Definition

The aggregate of the change in unrealized holding gain (loss) and foreign currency gain (loss) included in earnings during the reporting period.

+ References

No definition available.

+ Details

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- Definition

Tax on net realized and unrealized gains (loss), trading securities

+ References

No definition available.

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- Definition

Trading Securities, Realized Gain (Loss), Total

+ References

No definition available.

+ Details

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